René is in the backroom, jamming the little door to the cuckoo on the cuckoo clock and hiding the paintings (concealed in packages of spaghetti) down his trousers, when Yvette enters the room. They have a quick cuddle, when Edith walks in on them. René explains the situation by telling her he is teaching Yvette to dance. When she has left, Edith informs René that monsieur Alfonse has just proposed to her. He complains that she is already his wife, but she points out, that she is the widow of his dead twin brother and technically, they are not married.
They both go out into the café, where they meet monsieur Alfonse. He also does not think they are married and he goes upstairs, where he will ask permission to marry her from her mother. When he has gone, Michelle enters the café. She tells René and Edith that London wants them to initiate "Operation Waterloo", the new plan by which to send the British airmen away. For the moment, they are "hanging around" the café, disguised as coats on the clothes rack. Michelle then tells them that the midget submarine will be around to collect them soon. She also gives them instructions, written on paper. In order for them not to fall into enemy hands, they will eat them, but they start chewing on them before they have read them, so Michelle has to tell them to read them first.
Colonel Von Strohm is in his office, trying on a new wig, when general Von Klinkerhoffen is announced. The colonel hides the wig in his desk drawer. When the general enters the room, there is a person with him, carrying a mine detector. The general orders him to go outside and the colonel, not knowing what a mine detector is, points out, that the office has already been hoovered. The general tells him what it is for and that it can also detect metal. The colonel assures him that there is no hidden metal in the office, but the general is not convinced. As they are talking, the lamp on the table is moving, without their noticing it, as if to "hear" what they are saying. The general also looks in the desk drawer and, thinking that the wig is a rat, beats the wig until it is "dead".
It turns out, that somebody was listening in on them, namely the two Gestapo agents Otto Flick and Engelbert Von Smallhausen. Herr Flick suspects that the general has lost some gold and that René is the guilty party, since he is the only one who would dare to do it. In order to interrogate him, they will lure him into talking, by making Helga pose in lustful clothes before him. Von Smallhausen is therefore sent to get her.
When monsieur Alfonse is asking Fanny's permission to marry Edith, René enters the bedroom and asks Edith to marry him instead. Not listening to monsieur Alfonse's protests, he decides to go and book the registry office for the next day. Edith points out that the mayor is dead and the deputy mayor turns out to be - monsieur Alfonse, who is not at all happy about marrying the woman he loves to the man he detests.
Herr Flick is playing the violin, when Helga is brought into his headquarters. She is dressed in a robe and when herr Flick asks her if she is wearing something "teasing and tentalising" underneath, she says no - and she will not show him. He asks Von Smallhausen what she is wearing and he says he will not tell either, but he tells him of the effect it has had on him - and lets out a scream. When he has left, herr Flick asks Helga to show him her technique and then she reveals what she is dressed in underneath - making him also let out a scream.
At the café, René gives the paintings, in the spaghetti packages, to colonel Von Strohm and lieutenant Gruber. He also gives them some "empty" packages. The next moment, captain Bertorelli enters the café, wanting to play with the girls, but René says no to this. Then, Edith comes down showing how she will be dressed at the civil wedding. The colonel asks what wedding she is talking about and when she tells them that she and René are getting married, Gruber is somewhat upset to once again hear that René, whom he fancies, is to be married to another. He laves the café, but Bertorelli is glad to hear of this news and promises to make the wedding breakfast. Therefore, he picks up the packages of spaghetti and wants to cook them. The colonel saves the paintings by saying they are dynamite.
Later that night, Edith is preparing a special surprise for René in the backroom. He comes in and tells her he is going out on his stag night. While they are talking about this and René tells her not to use any of the Christmas puddings (since they are plastic explosives), Mimi, Michelle and Yvette peak in, all dressed as rough working men, and tells René to join them for the stag night. Then, monsieur LeClerc enters the room, dressed in a dyving suit. He is soon followed by the airmen, also dressed in dyving suits. They go out through the window, going off to launch "Operation Waterloo". René then goes off to his stag night.
The next morning, Edith is glad and cheerful, but René comes downstairs with a pack of ice over his head - aching from a hangover. When Edith has gone upstairs, Helga enters to try to drive René wild with lust and desire. This is to no avail, since he is too hung over to take any interest. She angrily leaves the café, bumping into officer Crabtree, who enters. He informs René that "Operation Waterloo" has failed, since the tide went out and the submarine is stuck on a sand bank. London will soon drop a collapsible dinghy, for another plan to be carried out.
At the mayor's office, monsieur Alfonse performs the wedding service, but he cannot make himiself say the words "man and wife" - his dicky ticker sets in. After he has been allowed to sit down and given a brandy, it is decided they should all return to the café. On doing so, captain Bertorelli complains that they are too early. It is pointed out, that monsieur Alfonse can perform the ceremony in the café, but before he can complete it, Bertorelli announces that it is time to eat. He begins with his surprise - which turns out to be four Christmas puddings that he found in the cellar. Not knowing that they are plastic explosives, he lights them. When the others do not manage to put them out, René throws them out into the square, where they explode - right next to Gruber's new "big tank".