Conrad Crusenhielm is a Count who is engaged to be married to Margareta. During his bachelor party he is hit on the head and loses his memory. Deserting Marine private Karlsson beats him up and changes clothes with him and makes it look like Conrad Crusenhielm has been murdered. Some other marines find Conrad and, since he is dressed like a Marine, they think he is the Marine 325 Karlsson, and he can't prove he isn't since he lost his memory. During a voyage to a foreign country, he must be taught everything about being a Marine, including not to speak snobbishly. During the voyage, he encounters many events, particularly the Corsican girl Lucretia, whom he will not be able to explain to his fiancée Margareta, if he would regain his memory.