Muggs is tricked into entering a Civilian Conservation Corps camp by Danny in order to get in shape. Muggs resists and battles with the camp captain and with other campers. He also becomes involved in trying to help one of his friends get out of trouble.

A group of young men who work at an aviation factory begin to suspect that a doctor who runs an air ambulance service is secretly a spy transporting secret information from the plant to enemy agents.

Copy boys Muggs and Glimpy investigate a murder. They locate the ex-wife of the murdered man and become convinced she is innocent. They hide her from the police while they investigate.

Muggs and Glimpy, two East Side Kids in the army, return to their neighborhood, supposedly on furlough; actually, Muggs has been honorably discharged with a physical defect, but he tells no one of this. Danny, another East Side kid, is in jail because a large amount of medical supplies have been stolen from the warehouse where he works. Muggs see Spider, a new member of the gang, flashing a large amount of money around, and Muggs shrewdly turns toughie, boasting that he has a dishonorable discharge because of thievery. This leads Spider to confide in Muggs that he is the one who has been aiding in the theft of supplies from the warehouse, and he gets paid for the loot by Larry, operator of a nightclub where Muggs' sister, Milly, is an entertainer. Fingers, a henchman for Larry, kills Spider when he learns that Muggs has been let in on the operation. The police then suspect Muggs of killing Spider.

A group of delinquents on their way to summer camp get stuck in a haunted house.

The East Side Kids discover that one of their own, Danny, is torn between staying in school and becoming a boxer, and is getting mixed up with gangsters.

The East Side boxing champion Muggs answers a challenge to a fight against the West Side champ but just before the match he is kidnapped. His friend Danny Lyons takes his place and wins the fight, only to have Mugs believe that Danny was responsible for his kidnapping.

In ridding the area of muggers, the East Side Boys acquire a wealthy benefactor whose privileged son, unbeknownst to him, has fallen in with thugs.

The gang is sent to the Wilton Reform School after they are unjustly convicted of stealing a truck. Bill Collins, brother of co-leader Danny, becomes involved in a killing and, while also innocent, is convicted and sentenced to death. Through a series of events, Muggs, Glimpy, Danny and the rest of the gang, learn that Knobby, a henchman of Luke Manning, knows something about the murder.

After living all his childhood in the street, a young boy rapidly notices that crime doesn't pay, leading him to become a policeman. One day, one of his best friends goes to prison for a murder he didn't commit. The policeman tries his best to release the friend by proving his innocence.

Rejected by the Army, Marines, and Navy for being too young, the punks help the war effort by throwing fruit at a shop they believe is owned by a Japanese American. Confronted by him wielding a short sword, the gang decides to come back at night but find him dead.

After having been framed by gamblers, Muggs is barred from riding in horse races. Snce he can no longer race, he takes up a collection so Ma Brown, who owns the horses won't have her stable foreclosed on. However, one of the gamblers involved in the frame falls for Ma Brwn's daughter, and decides to come clean and confess to the police about the frame. The other gamblers hear about it and set out to shut him up and discredit Muggs and Ma Brown once and for all.