Prologue: An underground agent named Lisa is smuggled into camp. She tells Hogan that there is an abandoned mine a mile from camp that is being built up by the Germans. A construction team has put in a heavy steel door and a sentry box, and they are camoflauged. Hogan thinks that there may be something permanent coming there. Newkirk is very smitten with Lisa, despite his just meeting her.
Part One: A Luftwaffe general named Metzger comes into camp and tells Klink that he is using the abandoned mine near camp as a hiding place for arms and ammunition; this is to be one of several places around Germany and this is under Hitler's orders. He says that he has a load of arms in a truck that accompanied him and that Klink is to provide a 24-hour guard at the mine. Hogan does not buy that the mine is for arms and ammo. He has Kinch ask London for info om him and he gets that he is second in command with the occupation forces in France and he hasn't been seen for three weeks. Kinch asks why Hogan is so sure that it's a scam and Hogan says that his instinct doesn't buy Metzger's story, and that a look inside the truck would help. The next day, LeBeau and Carter clean Klink's office while Schultz takes a nap in the desk chair; he says he ate too much at a party the night before. When he falls asleep, they pretend to mop up water on the wall; Schultz wakes up and they tell him it is from a leak in the roof. They say he should report it, but Schultz refuses to. Later, they tell Klink about it, he knows nothing, and they convice hin to let them do it. While they are on the roof, LeBeau gets down, and Carter tosses down a roll of shingles. LeBeau then pretends that he hurt his ankle, they get Schultz to get a stretcher and the guard guarding the truck to put him in the driver's seat. When they leave, LeBeau goes into the truck to see what's inside. When Schultz returns, Kinch and Carter say that Hogan took him back to the barracks; Newkirk pretends to be LeBeau under covers. When LeBeau gets out of the truck, he goes back on the roof. Kinch points this out to Schultz, who goes back in the barracks and finds that there is no one on the bed.
Part Two: LeBeau angrily comes in the barracks and tells the others that the truck is loaded with art. He produces a solid gold snuff box from the 18th centruy and an ivory fan at least 200 years old; the ivory has turned yellow. Hogan then says that Metzger has 'collected' these from his post in France to save until after the war, even if the Germans lose. He says that the top brass are the only ones to steal openly, others have to hide them. LeBeau wants to get them away from Metzger; when the others object, Hogan reminds them that this is part of their job: to 'harrass injure the enemy.' Later, Lisa and two other men, Karl and Walter, come into the camp. Hogan's plan is to have Karl and Walter dress as soldiers under Metzger. They are to take the truck with and order the guard and the driver with him back to camp. London is to provide a fake commando raid with dummies being dropped as a diversion, and smoke bombs from Carter to blow open the entrance to the mine. They are to order the men into the woods to fight the commandos and then they will load all the art in the mine into the truck and drive it to Amsterdam, where the underground has a safe house to hide it. Kinch gets some army papers for Karl and Walter to have to look authentic. When the truck leaves, the men go to work. Carter starts the smoke as the dummies are dropped. Klink is called about the raid and orders all his men into the woods. Karl, as an officer, orders Schultz away from the mine to fight the raid. Carter blows the entrance to the mine and they get the art into the truck. It turns out that Klink's men shoot at Schultz. When they leave, Karl kisses Lisa and Hogan tells Newkirk she is married to Karl. Later, Schultz tells Klink what happened and Hilda tells them that Metzger is coming. Hogan tells Klink to stand up to him. Metzger says that he will order an investigation and Hogan says that Klink has a bad temper and will be unhappy if Metzger does. He then says that Klink was going to call Hitler to complain and then suggests that he call; Metzger decides not to and leaves.
Epilogue: Outside Klink's office, Metzger tells Hogan that he saw the dummy commandoes. He asks where he can find his 'ammunition' and Hogan says, 'In a museum, after the war.' Metzger says he will order an investigation, and Hogan says he won't because 'When you steal frome a thief, one sure thing. You'll never call the cops.'