An emergency mission leads the Seaview to rescue Kowalski's brother Stan. Once on board, Stan's refusal to help anyone else threatens the sub's survival after it sinks to the ocean floor, a thousand feet below it's crush limit.

Admiral Nelson wanders the Seaview and finds it abandoned except for Captain Crain and Chief Sharkey. He has no memory of what happened before or what the strange sounds over the intercom mean. Capt. Crane is also trying to kill him.