An old man, adrift at sea, is rescued along with a sack of toys by the Seaview. The toys take on a life of their own and begin to sabotage the ship. The toys appear to be connected to an alien space ship lying on the ocean floor.

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.