René is sitting in the backroom, painting what looks like a baton. He informs the audience that it is the four gold bars, that he stole, which he has melted down into a new weight for the café's cuckoo clock. When he hangs it up, it is too heavy for the cuckoo, which starts "cuckooing" far more frequently than it should.
Edith enters the café, showing René her new hat, that she has bought. She says they do not have to think about money, now that they are rich (having, as she thinks, four bars of gold). She tries to find out from René where he has hidden the gold. As he refuses to tell her, she says she will make him tell her - by buying a see-through night gown at madame Lenard's, with which to tease him. When she has gone, Yvette enters the café, showing René her new silk stockings. She also tries to make René reveal where he has hidden the gold and when he refuses, she also decides to buy the see-through night gown at madame Lenard's. As Edith told René that she only had one left, he tells her to order it by telephone, when colonel Von Strohm, lieutenant Gruber and private Geerhart (Helga) enter the café to have a "serious talk with [René]". Yvette just misses the night gown and is very down-hearted because of this.
Gruber is a bit sad over the loss of his little tank and "the finger of suspicion" is pointing at René. They have decided not to investigate the whereabouts of the missing gold bars, if René helps them. They inform him that general Von Klinkerhoffen has taken the statue in which they have hidden the paintings and placed it in the chateau. He is to give a party for the generals who are planning the invasion of England and at this party, "The Excelsior Quartet" will be playing. René and the rest of the café gang will take their place, set up the orchestra near the statue and nick the paintings while pretending to play (by touching their instruments while Helga plays a grammophone record in a nearby room).
Von Smallhausen, being only a provisional member of the Gestapo, has applied for grade 3 officer. Herr Flick is the executor when he takes the test and he manages the question test (in which he has chosen the subject "Hitler"), but fails the physical test, only by showing his body. Then, herr Flick tells him about the general's party and that he thinks this is another meeting for planning the assassination of Hitler. Therefore, the two of them are to disguise themselves and join the party, in order to take names and photographs of those present.
Fanny has learned that René has a fortune in gold and is therefore very friendly towards him, thinking Edith ought to marry him at once. As the whole café gang gathers in Fanny's room, London calls on the radio, informing them that the Germans have a new machine for coding messages, called "Enigma". They are further instructed to tell Michelle to steal it from the chateau. Suitably, monsieur LeClerc enters the room, telling them that Michelle is downstairs, wanting to talk to them.
Downstairs, Michelle is glad to hear the news that they are to be disguised as "The Excelsior Quartet", giving them a good pretext to enter the chateau. Mimi will be concealed inside the double base case, sneak off to the room where the Enigma machine is and throw it out the window, where it will be captured by waiting resistance girls. With this, she is satisfied and leaves, after which Edith comes up with the plan of concealing a person inside the piano, place it near the statue and that way easily nicking the paintings. René does not think it will work, since he will play the piano, Edith will play the violin and monsieur LeClerc will play the cello while Mimi is hidden in the case. Yvette volunteers to hide inside the piano, but they would still need somebody to open its lid and somebody to play the double base. They are short of two people, but at that same moment, two people enter the café - officer Crabtree and monsieur Alfonse.
At the party, Gruber places the piano near the statue and informs Von Strohm of the café gang's plan. The next moment, "The Excelsior Quartet" enters (LeClerc and Crabtree in suits, Edith also in a suit and with a moustache and René in a gown). They take their places by their instruments, while Yvette and Alfonse are hidden inside the piano. Meanwhile, herrs Flick and Von Smallhausen also attend the party, disguised as waitresses. Von Smallhausen has a camera hidden under his left boobie, to capture pictures of everyone at the party. Michelle is also there, disguised as a German private. While the gang are playing, she tells Mimi that the coast is clear and that she should come out of the case. She cannot, since the case is locked. Secondly, Crabtree, who was supposed to have the key, has lost it, so Mimi cannot get out. She then crashes her feet through the case wall and punches three holes in the lid (two for her arms and one to see through). Then, she goes into the general's office to steal the Enigma machine.
The general complains that Gruber has placed the piano in front of the statue, so nobody can see and admire it, and therefore has it moved. When René tells this to Yvette and Alfonse, they lift the piano and walk towards the statue with it. Half way there, they stop, because the elastic of Yvette's nickers snaps. She therefore has to walk on with her nickers around her ankles and this makes monsieur Alfonse's dicky ticker set in. While Mimi finds the Enigma machine and drops it out a window, Yvette and Alfonse manage to nick the paintings. René then advices against Edith's singing the song they are playing (Louise), but instead, Crabtree starts singing it, in his broken French.