Ross Martin is a new recruit for the Michigan State Police troopers. He and his partner, Jim Burton, are assigned to the area of Crow River, where Ross's girl friend, Mary Adams, is the telephone operator. Crow River sheriff Pete Arnot, who also sells fishing bait, gives Professor Anthony, a new resident, a tour of the control room at police headquarters, where the police broadcast orders and maneuvers by radio to their patrol cars. Later, Mary transfers a call from Anthony's daughter Nan, who says she will be arriving soon at his cabin and that she has "thousands" of memories from her trip. In actuality, Nan is part of Anthony's gang, who have just robbed a bank. Ross and Jim are radioed to capture a grey sedan, whose occupants are suspected of the robbery. Nan, at the wheel of the sedan, is also being followed by rival gang members, until her thugs shoot at them, killing them and causing their car to crash. Ross continues to follow the sedan until it emits a smokescreen. He later stops by Anthony's cabin. Anthony has already discovered that the robbery money was marked and has burned it all. He and Nan adopt a nonchalant air and even allow Ross to inspect their garage, where the grey sedan, now painted another color, is parked. Another day, Ross pulls Nan and Anthony over for running a stop sign and becomes suspicious when he finds out the car is equipped with a flop-over license plate, smokescreen, loaded gun, and police radio, and has been freshly painted. He takes them to Pete's office, but no one is there, and the fugitives escape after knocking him out. The sergeant forces Ross to turn in his badge for losing his prisoners, and asks him to face the trial board, but Ross, having lost heart, becomes an auto mechanic instead. Anthony and his thugs rob a local bank, after cleverly calling the police about a fake explosion, and then sneaking in and destroying their radio station. They also kidnap Mary, so that the telephone system will be useless. The robbers elude the police, until Ross steals a police motorcycle and chases after them himself. In the meantime, the police call the Massachusetts police and ask them to broadcast to all patrol cars, as the Massachusetts police use the same radio wavelength as Michigan. After realizing the robbers intend to get to an airplane near his and Ross's favorite diner, Jim sends a message, via Massachusetts, to Ross telling him to pick up two "apple pies," aware that the robbers are also listening in. Ross understands the message and captures the robbers, and Jim appears with a transport to take them to jail. The sergeant reinstates Ross to the force, and he and Mary are reunited.