Danny and Kay Orlis are asked to go along on a chartered boat cruise off the coast of Guatemala to help translate for the captain and lead Bible studies for the crew. They take along Matt and Mark, twin sons of coworkers at the mission. But something fishy is going on with one of the passengers on this boat and his interest in an old shipwreck. Mark, Matt, and their new friend Gil try to discover what their shipmate is up to and solve the mystery of the wreck below.