Dark Day in the Deep Sea

This children's novel follows siblings Jack and Annie on a time-travel adventure to the 1870s, where they join a historic ocean expedition and learn a lesson about compassion.

Jack and Annie, a brother-and-sister pair from Frog Creek, Pennsylvania, are biking home from the library when a seagull swoops overhead, a sign that the magic tree house has returned to the Frog Creek woods. The tree house is a magical structure that can transport them to any time and place in history. They climb up to find Teddy and Kathleen, two young sorcerers from the legendary realm of Camelot, waiting for them. Teddy and Kathleen explain that Merlin the magician has an unspoken sorrow, and Morgan le Fay, a magical librarian, wants Jack and Annie to find a third secret of happiness before they can visit him. Morgan believes four secrets total will help Merlin recover. Kathleen hands them a research book titled The Deep Sea. Before departing, Jack confirms he has the Wand of Dianthus, a silvery unicorn-horn-shaped wand Merlin awarded them on a previous mission. Its three rules are that wishes must be only five words, the children must try their hardest before using the wand, and it can only be used for the good of others. Jack points to the book's cover and wishes to go there, and the tree house spins and transports them.

They arrive in a tall tree near a misty ocean shore. As the mist clears, they spot a large wooden ship with three tall masts offshore. Reminded of a past encounter with pirates, Jack panics, and they race back to the tree house. From the window, they watch three men row a small boat ashore: two sailors in white uniforms and a third man carrying a butterfly net and wearing a suit and bow tie. Convinced the men are not pirates, they climb down. Jack reads the ship's name, HMS Challenger, and looks it up in the research book. He learns that HMS (Her Majesty's Ship) Challenger was the first dedicated scientific exploration ship in history, sailing from 1872 to 1876 and circling the globe. This tells them they have landed in the 1870s.

Jack and Annie approach the men on the beach. The man with the butterfly net introduces himself as Henry, a friendly scientist with a long mustache who is part of the expedition's team trying to solve what he calls "the riddles of the deep." The two sailors are Joe and Tommy. Annie and Jack claim to be vacationing with their family nearby. When Annie asks to visit the ship, Joe and Tommy object, saying the captain would never allow children on board, but Henry persuades them, arguing that the children are bright and curious. They row out in choppy, graying weather. During the ride, Joe and Tommy mention a mysterious sea monster that some crewmen reportedly glimpsed in these waters.

On deck, Henry introduces them to the captain, a tall man in a white uniform, and Professor Thomson, the genial scientific director of the expedition. The captain orders the children removed from the ship, but before they can leave, a squall arrives and everyone is sent below deck. Henry leads Jack and Annie to the ship's interior, which has been converted from a warship into sea laboratories. Henry's lab is lined with bottles containing preserved specimens and ooze, the scientific term for deep-sea mud. Annie picks up a gleaming nautilus shell on the table. Henry explains it is not a specimen but a personal treasure. He grew fond of the small nautilus that once lived inside it, a creature that swam backward in a tub and squirted water at him. He expresses regret that the nautilus died, wishing he had returned it to the sea.

A bell summons them to lunch in the wardroom, the officers' dining room. Jack accidentally gulps his daily cup of lime juice, drunk to prevent scurvy, and spits it out in front of everyone. Too seasick to eat, he grows more miserable as the storm worsens. Henry directs them to go below to the hold, the ship's lower cargo area, while he secures his lab, but Jack, desperate for fresh air, runs up to the top deck instead. Annie follows. Giant waves crash over the deck, sweeping Jack overboard into the churning sea. Annie is washed over moments later.

Jack plunges into freezing water. His cork life vest keeps him afloat briefly before the waves rip it off. He realizes the Wand of Dianthus is in his backpack, left somewhere on the ship. Just as he is about to drown, something curls around his waist and lifts him to the surface. A giant octopus, a huge creature with a gray, umbrella-like body and yellow eyes, holds Jack in one tentacle and Annie in another. Jack tries to fight free, but Annie insists the octopus is rescuing them. Jack stops struggling and realizes the tentacle feels like a firm hug. Looking into the octopus's curious, shy eyes, his fear vanishes. The horn of the approaching Challenger scares the octopus, who releases them. Jack and Annie swim to the ship's ladder and climb aboard.

They explain that the octopus saved them, but the professor dismisses this, believing the creature nearly ate them alive. At the rear of the ship, sailors have snared the giant octopus in a net. The trapped creature turns bright red and releases dark ink. Sailors gather harpoons and weapons. The captain fears the creature could sink the ship, while the professor wants it brought aboard alive for study. Jack and Annie shout for the crew to release the octopus, but no one listens. Jack remembers the wand and races below deck with Annie. The backpack is not in the wardroom, so they find Henry and beg him to unlock his lab. Inside, Jack spots his pack on the table and pulls out the wand.

Jack wants to protect the octopus permanently, not just save it this once. He closes his eyes and speaks his five-word wish: "Make them hear the truth." They rush back to the deck, where a sailor hurls a harpoon at the octopus and narrowly misses. Annie cries that the magic is not working. Then the octopus raises its head from the water and produces a series of strange, otherworldly sounds. The crew falls silent in awe. Annie translates: "Let me go home. I'm no monster." The sailors declare it a sign, and the captain orders the octopus freed.

Henry requests permission to cut the creature from the net. Jack, Annie, Henry, Joe, and Tommy lower a small boat and row out. Henry slices through the net while Jack and Annie pull it into the boat. The octopus's color fades from red back to calm gray. Annie says good-bye, and the octopus lifts two tentacles as if waving before slipping beneath the surface. The crew breaks into applause, and the captain orders the ship to leave the area undisturbed.

Joe and Tommy row Jack, Annie, and Henry back to shore. Henry gives them his treasured nautilus shell and tells them they taught everyone an important lesson: It is a dark day in the deep sea when innocent creatures are made to suffer. He says that while the professor believes fears can be conquered through knowledge, Jack and Annie proved that fears are best conquered through compassion for all living creatures. He adds that his compassion for the small nautilus made him very happy. Jack recognizes this as the third secret of happiness they have been seeking.

Henry salutes them and returns to the rowboat. Jack and Annie walk back to the tree house. Annie uses a book about their home state of Pennsylvania, kept in the tree house for return trips, to wish them home. The tree house returns them to the Frog Creek woods, where soft rain is falling. Jack stores the nautilus shell in his backpack as a reminder of the secret: compassion for all living creatures. As they ride their bikes home through the rain, they joke about the octopus, whom Annie names Charles, and imagine him returning to his own family.