In Magic Tree House: Dolphins at Daybreak by Mary Pope Osborne, siblings Jack and Annie embark on their first mission to become Master Librarians. Morgan le Fay sends them to a dazzling coral reef, where they must solve a mysterious riddle. Exploring the ocean in a mini-submarine, they encounter fascinating sea creatures—but danger strikes when a hungry shark appears and the submarine springs a leak! Forced to swim in the open sea, Jack and Annie are rescued by friendly dolphins who guide them to safety. Through this thrilling underwater adventure, the young heroes discover courage, quick thinking, and the wonders of the ocean world.
