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Jack and Annie continue their quest for the secrets of happiness–secrets they need if they’re going to save Merlin. But when the magic tree house leads them to a tiny deserted island in the middle of the ocean, they’re not sure who needs help more–Merlin or themselves! The brother and sister team are soon rescued by a ship of explorers and scientists. But the crew isn’t looking for the secrets of happiness. The crew is looking for . . . a sea monster!

128 pages, Hardcover

First published March 25, 2008

About the author

Mary Pope Osborne

965 books2,380 followers
Mary Pope Osborne is an American author of children's books and audiobook narrator. She is best known as the author of the Magic Tree House series, which as of 2017 sold more than 134 million copies worldwide. Both the series and Osborne have won awards, including for Osborne's charitable efforts at promoting children's literacy. One of four children, Osborne moved around in her childhood before attending the University of North Carolina. Following college, Osborne traveled before moving to New York City. She somewhat spontaneously began to write, and her first book was published in 1982. She went on to write a variety of other children's and young adult books before starting the Magic Tree House series in 1992. Osborne's sister Natalie Pope Boyce has written several compendium books to the Magic Tree House series, sometimes with Osborne's husband Will Osborne.

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5 stars
2,029 (42%)
4 stars
1,373 (28%)
3 stars
1,074 (22%)
2 stars
249 (5%)
1 star
101 (2%)
Displaying 1 - 30 of 182 reviews
Profile Image for Scottsdale Public Library.
3,413 reviews328 followers
August 7, 2024
Set sail on a pirate adventure with Jack and Annie as they search for hidden treasure. The story is filled with swashbuckling action and historical insights about pirates. The thrilling plot and well-developed characters make it a page-turner. This book is perfect for young readers who love adventure and tales of the high seas. -Teen Volunteer Adhyyan R.
Profile Image for Kathryn.
4,610 reviews
March 1, 2022
I personally never get too excited about these books, but my eight-year-old really enjoys them and that's what matters. I do think they're a good fit for this age group as they provide some education and adventure in an easy-to-read way. In this installment, we get a look at ocean exploration in the 1800s and meet a "sea monster" (giant octopus) whom Jack and Annie must save from the men who want to destroy it. They try to explain that animals have feelings and deserve to be free. The book might be a bit much for sensitive young audiences as there is a quite a bit of peril, first for Jack and Annie and then for the octopus. However, children looking for an exciting adventure story, with some heart, should be pleased.
Profile Image for Charisse.
79 reviews41 followers
May 22, 2012
We learn that deep under the sea, there are dangerous sea animals like the octopus and sharks.
Profile Image for Zack.
50 reviews2 followers
December 4, 2013
I loved this book! Mary Pope Osborne really catches your imagination. She tells facts and fiction at the same time. You will keep on reading it because it catches your attention like a flytrap. In this book, Jack and Annie go back in time and save a giant octopus. I love the ocean because it is a totally different world, which Jack and Annie get to experience. If you read this book, I bet you will love it, too.
48 reviews
January 4, 2018
Personal Response:
I read Dark Day in the Deep Sea . I thought the book was okay, because I found the book too kiddish. I found this book to be kiddish, because I knew the magic tree house can’t be real.

Plot:
The book started off when Jack and Annie were in the treehouse, where they were about to pick a book. The book they chose was about the the deep sea. It was about Jack and Annie trying to find the present of happiness in the sea. They arrived there, and saw sailors are on a ship called the Challenger, and they were trying to find a monster in the sea and dispatch of the creature. Jack and Annie had a wand that was like a shell. Jack and Annie also received a wand, to only use after they tried their best to keep the monster alive. They also wanted to keep the monster alive, because it was the present of happiness, which meant the happiness of the sea was being free.

Characterization:
In the book, there were two main characters. One character was Annie, and she was seven years old in this book. Annie had long, blonde hair. The other main character was Jack who was 10 years old in this book. Jack had short, brown hair and wore glasses. Annie had more of the go-getter attitude and really wasn't afraid of going to do things. Jack had a attitude of stepping back and looking at all of the possibilities that could of happened.

Setting:
The two kids lived in Frog Creek, Pennsylvania. It was summertime and in the afternoon. Then the magical treehouse went to the sea. In the sea, it was very warm and was sunny. The importance of the 1800 was to show what it could've been, what the explorers were thinking, and how they thought about the new world.

Thematic Connection:
The main theme for the book was working together and another was to help someone who was in need. This was evident by helping the sailors find the the happiness of the sea. Jack and Annie worked together to find the book.

Recommendation:
I recommend this book to elementary students who are just learning to read, like third graders and up. This book does not pick a certain gender so it can be for both genders, because this book appeals to girls by having Annie in the book. It also could be recommended to guys because Jack was in the book. This book helps show that reading could be fun and interesting.
Profile Image for Christopher Salcedo.
13 reviews3 followers
July 6, 2012
I like this book because in the book it states, Jack and Annie of Frog Creek, Pennsylvania, know they have to find one of the four secrets of happiness to help save Merlin the magician. But when the magic tree house whisks then off to a misty island in the middle of nowhere, they wonder how they will find anything. As the fog lifts, they see a huge three-masted ship-could it be a pirate ship? When a small rowboat makes its way to shore, the three men inside don't look like pirates at all.(pg.1) Another reason I like this book is because in the book it states, you might think I spent every summer playing in the water. But sadly, I was afraid of the ocean. Only as a grown up did I realize that the creatures of the sea were probably more afraid of me than I was of them. Since learning this, I have not been afraid- in fact, I'v gone snorkeling in the waters of the Caribbean and have swum with dolphins off the coast of Mexico.(pg.68) The last reason I like this book is because this is A MERLIN MISSION book. A MERLIN MISSION book are the latest books in the Magic Tree House series. They are different from the other books in many ways.(PG.100)

Someone who would like this book is my cousin Natalio Duran. I know that he would like this book because he likes books that have a ocean in it and he also likes THE MAGIC TREE HOUSE books. I know that he (Natalio Duran) likes THE MAGIC TREE HOUSE books because when I went to his house one time he had a bunch of MAGIC TREE HOUSE books when he was only reading one of them. He would also like this book because it has action/adventure. I know he likes action/adventure books because first, he likes action/adventure games, and movies.

One challenging aspect of this book is when a Octopus was on top of a boat and it was helping Jack and Annie. I say that is a challenging aspect of this book because the way that part of the story was told, because first it says the Octopus was chocking Jack and Annie, then it says the Octopus was helping the children (Jack and Annie). Another challenging aspect of this book is the point of view says that first Jack is telling the story then it says Annie is telling the story. That is a challenging aspect in this story because it makes my head not understand the story a little bit.

A character that I can describe well in this story is Henry Moseley. Henry Moseley was a young man, in his twenties when the voyage began. He loved natural history and became one of the greatest natural scientists of his time. The chief scientist on the Challenger was Charles Wyville Thomson, a brilliant Scottish professor.Henry Gwyn Jeffreys Moseley (23 November 1887 – 10 August 1915) was an English physicist. Moseley's outstanding contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number.

8 reviews1 follower
August 21, 2012
I like the book Dark Day in the Deep Sea because I learned a lot of facts and it adventures."Water covers three-quarter of our earth.Most of the ocean is an enormous plain a little more than two miles deep.But some oceans trenches are more than six miles deep."#12 Another fact I learn was"The ocean is home to thousands and thousands of sea creatures.Mountains and volcanoes are also hidden deep beneath the surface of the sea."#12 The Dark Day in the Deep Sea is adventures"Morgan sent as to tell you about your next mission for Merlin's;said Teddy."How is merlin?asked Annie.Teddy stopped smiling.He shook his head.Merlin still suffers from an unspoken sorrow."Kathleen said sadly."#5
You would like this book if you like to learn because you can learn 4-5 facts in one chapther.For example #1:The HMS CHALLENGER'S (HMS challengers stand for Her Magesty's Ship) was a british navy vessel that severed as the first dedicated scientific exploration ship in the history of the world.#22 Another fact is"From 1872 to 1876 the HMS Challengers circled the globe; exploring the dark depths of the ocean.There were over 200 seamen and six scientist's on board.#23 That all for now.
One challenge from the book Dark Day in the Deep Sea was the settting.The setting was a challenge because in chapther 1: they were at home.Chapther 2: they were on the beach or something near the ocean.Chapther3: they were in or on the ship.Chapther 4:they were in the deep hole.That was my one challenge.
Jack and Annie are master librarians.Jack and Annie live in frog creek Pennsylvania.Two young Sorcerer's named Teddy and Kathleen are people jack and Annie found while helping save Camelot or mythical humanlike creatures and found valuable to also help save camelot.Jack is 8 years old.Annie is 7 years old.Annie and Jack work for Morgan.
Profile Image for Jean O'Shea.
30 reviews2 followers
November 10, 2008
Dark Day in the Deep Sea by Mary Pope Osbourne is the 39th installment in the early reader series. In each book, the protagonists Jack and Annie discover, in their local grove of trees, a magic tree house that whisks them off on an adventure. Generally, they have a book as a guide and an important task to complete. This series is aimed at the K-3rd grade set.

I love Magic Tree House series! I can always count on its pattern of chapters: discover the tree house and task, begin adventure with confidence, encounter a challenge and research a resolution, complete task and return home without time passing. There is always a successful ending, which is important for this age group. It is written plainly with uncomplicated sentence structure to support beginning and transitional readers. The way the author has set up their relationship with books for solving problems is one of the most important feature of this series. Another important feature of the series is the non-fiction companion supporting the science or history from the story.

Interest Level:
K-3rd
Age:
4-8yrs
Genre:
Fiction
Subject:
Adventure

Ellen Heath, Easton Area Public Library, Easton, PA:
The youngest patrons often ask for their favorite books by character, not title. Our beginning chapter-book readers still devour Mary Pope Osborne’s “Magic Tree House” books (Random) and Barbara Park’s “Junie B. Jones” titles (Random)—in order, please.
Profile Image for Maya Orama.
80 reviews2 followers
March 15, 2015
This story is about a girl and boy named Jack and Annie . Jack and Annie went into the library then out. Jack hid lots of books in his bag. Then they start to run. They both found teddy and Kathleen. Teddy and Kathleen told Jack and annie to take books from the library so the tree house can have more books in the magic tree house. They boo looked for a books that they wanted to go into. It was a pirate book. They wished that they were in it, then they got teleported on the ship of a pirate crew. They both introduced themselves. Then, when yo eased, they became best friends. The pirate crew sang songs, danced, and they ate with them. So then they said they needed to go hom. The captain gave them a gold coin, then waved goodbye. They couldn't wait for their next adventure in the magic tree house! THE END

Profile Image for Tricia.
937 reviews17 followers
July 3, 2009
As I was reading this, I thought "all right, this one really has dramatic tension, they really do get better as the series progresses." But then MPO took out a 2-by-4 and starting hitting us over the head with it. Oof. We get it! All life is precious! But how are scientists going to understand the sea and the creatures within if they can't study it? Anyway, too much preaching. Enthusiasm balloon seriously deflated.
Profile Image for Mary Lee.
3,155 reviews55 followers
April 13, 2008
My adult brain fought with the idea of the octopus speaking out loud to the sailors and early oceanographers. And while I agree with the *moral* of the story that one of the secrets to happiness is compassion for all living creatures, it seems like MPO has trivialized the way this could have been/can be/needs to be accomplished.
20 reviews1 follower
September 30, 2015
The book Dark Day in The Deep Sea by Mary pope is one of my favorites book that has been written.Jack and Annie continue there journey doing quests for Merlin.I like how they like to explore and always work as a team.Well anyway they have to find a source of love.But when they go on a ship things start to head there way and some things get bad.
Profile Image for Melissa Namba.
2,167 reviews14 followers
December 18, 2015
I really like the characters and how they don't change from book to book. This was one of the weaker books, because although they were on board a ship dedicated to science, the presentation would make any science teacher vomit. I mean, a talking octopus? Or one so huge that saves drowning children? Come on.
Profile Image for Emily.
188 reviews
March 31, 2020
In the magic treehouse series, not only in Merlin Missions, Jack and Annie found a magic treehouse. They soon discovered that in the magic treehouse there were lots of books and when they point to a picture in the book and make a wish to go there the magic treehouse just magically transports them there! They soon learned that the treehouse belongs to Morgan Le Fay from Camelot. Jack and Annie have helped Morgan with a humongous amount of missions in all places and time periods with the help of the magic treehouse. However in Merlin Missions it is not however Morgan that sends them on these missions. It is Merlin, a fantastic magician. During Merlin Missions, Jack and Annie make two friends named Teddy and Kathleen. They soon completed four missions that showed they could properly handle magic. On those missions, they were given a book of ten magic rhymes to use on four missions. Each rhyme can only be used once. Since they succeeded in those four missions they were given the Wand of Dianthus. A magic wand that could create magic. On this mission, Jack and Annie are going to find another secret of happiness for Merlin to cheer him up. They already found two secrets of happinesses so this is their third mission to find a secret of happiness. They have to go on four missions and find four secrets of happinesses altogether to cheer up Merlin.

In this book Jack and Annie were just getting home from the library when they saw that the magic treehouse was back! They went in and saw their friends Teddy and Kathleen! Teddy and Kathleen gave them a research book and then they said goodbye. Since Jack and Annie wanted to help Merlin cheer up, so they pointed at the research book and wished to go there. The magic treehouse magically transports them there as usual. Jack and Annie arrived at a beach. They decided to play in the water for a bit. Before long a boat came rowing their way. They have met pirates before, and they are not nice at all. They quickly ran to the treehouse, pulled the ladder up, and peeked out the treehouse window. However the people in the boat did not look like a pirate at all! They soon decided to say hi to them. They soon kind of made friends with a man named Henry. He is a scientist that studies marine creatures, and the things at the bottom of the ocean. Jack and Annie begged him to visit his ship so he said yes. Jack, Annie, and Henry got into the boat, and the two rowers began rowing them towards the ship. As the boat rowed back and fourth towards the ship Jack felt seasick. He was feeling very uncomfortable. Soon Jack, Annie, and Henry were on the ship. Unfortunately, the captain said children were not allowed on the ship. They had to do what the captain said. But then, before they leave, Henry decided to take them to his lavatory. They saw many bottles of dead animals, and things in the ocean. Jack put his backpack down as he turned to look at the skeleton of a tiny seahorse inside a microscope. However Henry said something was not caught yet. The monster. Soon it was time to eat. They had very disgusting food. Jack accidentally drank his lime juice too fast, and he spat it all out because it was too disgusting. The really big problem was that soon waves came crashing into the ship! Jack and Annie were thrown overboard! Soon, they were in the hands of a big gigantic monster Henry had mentioned! A gigantic octopus! They need to get out of the monster’s hands, but soon they realized the octopus was trying to save Jack and Annie from drowning. When Jack and Annie were back on the ship, they found everyone trying to kill the octopus! They need to convince them that he is not a monster, and they should not kill him! However it was no use. Everyone kept on planning to kill the octopus that had saved Jack and Annie’s lives! Jack and Annie can’t just let the captain and the other people kill him! They have to do something, but what are you they going to do!? Oh, and how are they going to find a secret of happiness when they are trying to convince people not to kill a gigantic octopus?
3 reviews
April 30, 2024
It was something.The setting of the HMS Challenger back in 1872 was a pretty good setting.I learned a valuable lesson today,to show compassion to animals.It starts out as a usual book.But then we see the sailors and Henry,who take Jack and Annie into the HMS Challenger,but only until the storm ends.Soon after,Jack and Annie fall overboard,get saved by the octopus,and have to save the octopus.The sailors try to kill the octopus,and the scientists want to study it,leading Jack,Annie,and Henry to the lab,where the bag sits.Jack pulls the wand out,and after reciting his wish,the octopus speaks.The sailors free the octopus,and the book ends when we're back in Frog Creek.
All in all,it was a good book.Gets a 4.1/5.
7 reviews
December 17, 2018
I like this book because it is interesting and it is about an adventure. This book is about two child one called Annie, and called Jack and their adventure in the deep sea. It is interesting because Annie and Jack is been held by a giant octopus, And that wouldn't happen in real life. So, I think that is interesting and fun. Also, Jack and Annie had a magical wand, called the Wand of Dianthus and when you use it, the spell need to be in five words. In real life, a magical wand don't exist. So, I recommend people who likes adventure to read this book and it is fun and interesting.
Profile Image for Kim.
1,254 reviews4 followers
February 18, 2021
Jack and Annie are transported to an island. There they meet a scientist who is researching the island. Jack and Annie ask to go onboard ship to have a tour. They receive a tour of the labs, the wardroom and they deck. They get washed overboard and are saved by an octopus. The sailors on board want to destroy the "monster" but Jack and Annie intervene. It's sad that others want to destroy something that they know nothing about. People fear the unknown...Jack and Annie found the next clue to happiness. You have to read it to find out.
725 reviews
July 13, 2024
Although slightly less realistic than some of the other books in this quartet within the Magic Tree House series, this was still an enjoyable read. The facts mixed in with the fiction were strong, although sometimes I feel Osborne might be slightly losing touch with her audience (some of the times when Annie says, "Yay!" seem forced), overall the book is still a strong addition to the series. I look forward to reading the next book in the series and highly recommend this series to its intended audience.
13 reviews2 followers
August 11, 2017
dear mary,
I love your books so much that just now I thought the magic tree house series is the best series
ever,please keep writing more books,because i wish i could have all your books and then read them
all in order.



love,
Eden p.
40 reviews1 follower
December 3, 2020
Mary Pope Osborne does an excellent job of catching your imagination within this book. This is a great book for Elementary students who are just getting in chapter books. It captures factual evidence while also engaging readers with the fascination of the sea. Although, this was not one of my favorite books to read because of the presentation. Certain details, like the talking octopus, just felt too kiddish for this audience.
Profile Image for Melainebooks.
1,868 reviews23 followers
Read
April 15, 2022
"La connaissance nous libérera de nos peurs. Mais vous nous avez rappelé que la compassion est le meilleur remède contre la peur. Nous, les hommes de science, devons rester respectueux des êtres vivants, quels qu'ils soient." "Un des secrets du bonheur, c'est d'être compatissant envers les êtres vivants, quels qu'ils soient."

Je pense que ces deux citations résument bien cette nouvelle aventure de Tom et de Léa. Attention, sa lecture peut vous donner le mal de mer.
Profile Image for Jamie.
301 reviews
June 10, 2022
It was nice to see that they were able to learn more about the ocean through the scientists, even though they felt like they knew enough about it already. How they handled the octopus situation was actually more thought out than I anticipated, definitely was not expecting the outcome.
On to the next one.
853 reviews2 followers
January 26, 2024
I thought this was a great children’s fantasy. I personally love octopuses. They love peoples and can, on some level, relate to humans. They develop relationships with people when in an aquarium. They do change colors, and they have a short life span. They can change their shape when they need to get through a narrow place. Very special creatures. CathyR
Profile Image for Leila.
154 reviews
June 4, 2024
It will always be a 5 stars for me this series has a special place in my heart and I’ve loved since I was in elementary school and I’m happy to be rereading the series again and waiting for a new book to be released in both series Merlin Missions and Magic Tree House, also brings much nostalgia from the 2000s even though it released in the 1990s.
Profile Image for Danna.
569 reviews
October 7, 2017
Who doesn't love the Magic Tree House Series? Great read for second and third graders about the creatures of the sea and those who have explored them. My students were engaged and involved in the book. Hopefully this is the hook to many more happy reading moments for them.
62 reviews
November 25, 2020
These are great transition books for kids. This is a way that kids are able to learn more about sea creatures and get excited about reading. The Magic Tree House series are some great books to keep in a classroom.
Displaying 1 - 30 of 182 reviews

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