Marine biologists Dom and Jake explore the deepest ocean trenches in the world, where they encounter unique sea creatures, in a book describing the history of deep sea submersibles and the sea life that lives in the deepest parts of the ocean.

After Owen captures an enormous bullfrog, names it Tooley Graham, then has to release it, he and two friends try to use a small submarine that fell from a passing train to search for Tooley in the Carter, Georgia, pond it came from, while avoiding nosy neighbor Viola.

Cory McNab is a member of the Navy's Marine Mammal Program where he is partnered with a search-and-recovery dolphin named Kaj, and their new mission is to help locate a spy submersible lost in North Korean waters--but first they have to win the trust of the Navy SEALs who are assigned to deal with the problem.