After a quayside mix-up with the Italian family of his fiancée, Able Seaman Knocker White finds himself literally left holding the baby. Unable to return it before his ship sails he enlists the help of best mate Puncher Roberts to smuggle the child aboard. But babies are surprisingly demanding and gradually the whole crew is drawn into helping keep it fed and washed – and undiscovered. Even so, the officers above deck start to puzzle over the increasingly strange happenings on board.