A few days after Pearl Harbor, failed Huxton entrepreneurs Stanley Laurel and Oliver Hardy close their bankrupt bicycle shop and go to enlist. The bumblers are rejected by every branch of the military, however, and return to Huxton, broke and depressed. Stan and Oliver then discover that, during their absence, their bicycle shop lease was turned over to newcomer Eustace Middling, who sells radios. When the affable Middling offers to share his store space, Stan and Oliver take him on as a partner, unaware that he is a German spy. Dan Madison, the local newspaper editor and head of the Huxton civilian defense team, then asks Stan and Oliver to post notices for that night's defense planning meeting. After eagerly plastering the notices around town, Stan, Oliver and their dog show up late for the meeting and disrupt a speech by influential banker J. P. Norton. Over Norton's protests, Dan invites Stan and Oliver to become air raid wardens and, as the culmination of their training course, they are required to participate in an elaborate drill. Although Dan has assigned Stan and Oliver an easy task, Stan accidentally picks up the wrong order and, instead of treating a policeman's imaginary splinter, Stan and Oliver must "rescue" Norton from an imaginary fire. In their zeal, the two manage to knock out Norton in earnest and bury him in a pile of sand. Later, the recuperating Norton demands that Dan dismiss Stan and Oliver, but Dan convinces him to give the men a second chance. Soon after Stan and Oliver receive their air raid warden equipment, they are called for a late-night drill and begin notifying citizens to turn off their lights. Unaware that the all-clear has sounded, Stan and Oliver order cranky Joe Bledsoe, with whom they had a previous encounter, to turn off his lights. Joe "invites" them to do the job themselves, and soon the three men are turning lights on and off so fast that a neighbor calls Dan to report spy activity in Joe's house. After Stan knocks over a large jigsaw puzzle that Joe was just about to finish, Stan and Oliver flee upstairs and lock themselves in Joe's bedroom. Joe breaks in and knocks Stan and Oliver out with a gin bottle, just as Dan's assistant, Capt. Biddle, arrives to apprehend the "spies." Smelling the gin on Stan and Oliver, Biddle declares them drunk and, over the objections of his reporter fiancée, Peggy Parker, Dan dismisses the men. Later, Dan tells the wardens that Major Scanlon is coming to Huxton to oversee a surprise drill. On the day of the drill, a depressed Stan and Oliver are lingering after-hours at their bicycle shop when Stan happens to hear two of Middling's cohorts talking German. Sure they are spies, Stan and Oliver hide in their car trunk and ride with them to their two-story hideout. While ensconsed upstairs, they then overhear Middling, whose real name is Mittlehause, and the spies's leader, Rittenhouse, planning to blow up the Huxton magnesium plant during the major's test. Stan and Oliver try to warn Dan of the impending disaster by attaching a note to one of the spies's carrier pigeons, but the bird flies directly to Rittenhouse. The spies quickly locate Stan and Oliver, and one of them is assigned to kill the intruders, while the others leave for the plant. Stan, however, accidentally knocks the killer out, and the men escape in a broken-down "flivver." Just as the other spies arrive at the plant and begin laying their explosives, Stan and Oliver reach a telephone and call the civil defense station. Thinking that Oliver's message is part of the major's drill, the operator relays his instructions to Dan and Biddle. Dan, Biddle and the defense team arrive at the plant in time to stop the explosion and capture the spies. As their final act, Stan and Oliver expose Middling, who is also an air raid warden, as a spy. Dan thanks Stan and Oliver for saving the plant, and the bumblers are happy to have at last served their country.