The film depicts Mickey Mouse working at a construction site under the supervision of Pete and Minnie Mouse singing a song called "Box Lunch" about selling box lunches to the workers. Mickey pays more attention to Minnie than to his work and causes several accidents that annoy Pete. Pete also flirts with Minnie, but she rejects him. When Mickey accidentally drops a load of bricks on Pete, the latter begins to strangle him, but the workers have their lunch break soon after. Mickey settles down to eat a fish sandwich, but it is stolen by Pete. Minnie offers Mickey a free box lunch, but Pete uses a crane to abduct her.
Mickey chases after Pete, and finally fights him high up on the building. Minnie grabs a pan of red-hot rivets and drops them down Pete’s pants, which gives the mice enough time to flee as Pete pours water down his pants. In the process of chasing Mickey and Minnie, Pete has an anvil fall on his head and fires rivets at them with a handheld pneumatic hammer. This turns on him when the hammer falls into his pants and gets attached to his peg leg. The mice escape down a chute riding a wheelbarrow, while Pete falls into a cement mixer, and accidentally dismantles a large portion of the building. Enraged by the damage, Pete angrily fires Mickey, but the latter doesn't care as he immediately goes into business with Minnie selling box lunches.
