"Ari's dad is a Marine Biologist and has invited Ari, Zeke and Jez to a trip out to sea to track dolphins for his research. With awesome new scuba skins and a ride in the submersible, Ari and his friends get to explore the ocean and swim with the playful dolphins. But something lurking deep beneath the surface decides to make its presence known, and Ari must find a way to save his dad and friends from danger without becoming prey himself!"--Publisher's description.