Jerome K. Osborne, chairman of lumber production for the Department of National Defense, calls in Dan Crowley of Crowley Lumber and asks the lumber magnate why his government deliveries are late. Crowley tells Osborne that a series of strange accidents has been happening at his mill. When Osborne threatens to cancel his government contracts, Crowley offers to oversee the mill's operations himself. Back at the mill, Crowley meets with his two foremen, Quebec and Arizona, who tell him that some poor workers have been holding up production. The foremen are then allowed to hire new men, one of which is their old friend, Kansas. When the fired men, led by Jules Fabian, try to start a fight with Arizona, Kansas steps in and defeats the entire group by himself. The three friends then go to the lumber camp, where they meet French-Canadian Pierre Lacour, his sister Yvette and his slow-witted friend, Bill Cormack. The two men are soon hired to work as lumberjacks, and Kansas quickly falls for Yvette. Later, Pierre tells Kansas that he has worked at a number of lumber camps and suspects the existence of a group of saboteurs, which he believes is now working in this camp. Pierre's suspicions are correct, as Fabian heads a group of foreign agents, and the saboteurs quickly discover that Kansas is actually a special agent for the Forestry Service. That night, a jealous Arizona orders Kansas to break his date with Yvette and drive the evening truck run. When Kansas decides to keep the date anyway, Pierre takes the run instead and is killed when his truck is apparently forced off the road by another vehicle. After Pierre's funeral, a grief-stricken Cormack tries to kill Kansas, as the saboteurs have told him that Kansas was responsible for his friend's death. Later, Kansas goes to explain things to Cormack, but finds the mentally handicapped man murdered. Mill supervisor Joe Radway immediately accuses Kansas of the killing, but Quebec and Arizona vouch for their friend. After a second truck crashes, the drivers threaten to quit, so Kansas, Quebec and Arizona offer to take their places. As Quebec turns on the siren of the lead truck, Kansas, riding in a second truck, realizes that the mystery car is actually a sound-activated mechanical mirror. Kansas manages to board the truck and convince Quebec to drive through what appears to be oncoming headlights. Afterward, the three friends confront Radway, whose mechanical toy triggered Kansas' discovery. Learning that Radway purchased the toy from merchant Doc Turner in St. Martin, the group heads there, but not before Radway's secretary, Ann Barrows, warns the crooked storekeeper of their imminent arrival. Turner sets a trap for the lumbermen, but the saboteurs, including Turner, Radway and Fabian, instead are captured by the three friends. In the meantime, Yvette manages to capture Barrows as well. Later, Kansas is put in charge of the mill, and his two old friends are soon fighting about which of them he will be directly supervising.