Ed Ramsey's girlfriend, Tracey, and his son, Frosty, just completed the training necessary to scuba dive. As a celebration, Ed invited them to join him on a weekend dive trip in the Gulf of Mexico, only to have it marred by tragedy: a diver goes missing and later is found dead on the sea bottom. However, what first appears to be a fatal accident turns out to be a case of murder, and Ed reluctantly finds himself entangled in the investigation. The murderer must be among the small group of passengers and crew on board the dive vessel, but the police can find no motive for the killing, which greatly complicates their ability to identify potential suspects. Ed, Tracey, and Frosty try to assist the authorities, which leads them into some harrowing experiences before the case is solved.