Hogan is outside Klink's office reading a newspaper when Klink tells Schultz and Hilda that General Burkhalter and Captain Ritter of Luftwaffe Intelligence are on their way. Upon seeing Hogan, Klink orders him out. Hogan sends in Le Beau and Carter, under pretext of cleaning duty, to eavesdrop on the meeting. They learn that Ritter has been ordered to acquaint himself with POW camp facilities. He also has a top secret Luftwaffe codebook, wrapped in plastic, and asks Klink to put it in his safe.
Naturally, Hogan is anxious to get hold of the codebook for London. So under pretext of cleaning windows, he and Newkirk make their way into Klink's office. Klink is lured out of his office with a phone call supposedly from Burkhalter while Newkirk opens the safe. Then Klink returns, having found that Burkhalter did not send for him and was angry at his nap being disturbed. Anxious to improve his efficiency rating, Klink orders a special formation to find five silver spoons that went missing from the officers' mess. This happens to be just as Newkirk is leaving Klink's office with the codebook. In order to avoid discovery, Newkirk throws the codebook down the well. The well is disused and dry, but they have to find a way to get the codebook back.
Hogan and Co blow up Hammelburg's waterworks to cut off the water supply to Stalag 13. This is to give them the pretext of digging for water in order to get to the well. They find the codebook, but then Schultz stops them for a spot check to find the spoons. They are forced to throw the codebook back into the well, which is now filling with water. The plastic will protect the codebook, but someone must brave icy water in order to retrieve it. Carter is chosen for the job while Le Beau creates a diversion with another escape. Carter retrieves the codebook and the code is soon on its way to London. Klink is persuaded to mitigate Le Beau's sentence in the cooler when the spoons turn up on his desk.