A number of people are held captive by Major Ling Wu and his men, who refuse to let anyone go until identifying a spy in their midst.

When he sends his assassin Sun Lee after one of the hostages, Dan Maynard, a doctor, and Knuckles Greer, a sailor, manage to intervene.

Ling tries to rape a young newlywed, Leah De Verno, and cuts the rations so that the captives have barely enough food to stay alive.

A young girl named Penny, daughter of another interned couple, requires emergency medical help and Dan appeals to his captors to permit him to operate on the child.

Dan finally becomes aware that Rita played no role in assisting their captors, and after he escapes and contacts the submarine, he goes back to rescue the others and her.