Dolphins at Daybreak by Mary Pope Osborne

The siblings travel to an ocean research center, where they explore a mini-submarine and get trapped underwater. With dolphins and a sea turtle coming to their rescue, they face danger from a hungry shark and limited air supply. Jack and Annie must stay calm and think fast to reach the surface safely. This ocean adventure combines marine life, environmental awareness, and a tense underwater escape. It’s a fast-paced and educational trip beneath the waves.