A boys club known as the East Side Kids, which is based in the Lower East Side of New York City, makes arrangements for their member Glimpy to appear as best man at his sister Betty's wedding. Gang leader Mugs arranges for a police escort by telling the police that a mob action will take place at the church, while several other Kids obtain a tuxedo and flowers at a funeral home. Just prior to the wedding, Betty's fiancé Jack buys a home at 321 Elm Street in the suburbs. He plans to honeymoon there, but reluctantly decides to sell when Tony, a real estate agent who is an operative for Nazi spies, tells him the house next door is haunted and gives him a cash advance. When Jack and Betty check into a hotel after the wedding, they get a call from Sarah Elwood, who used to live at 321 Elm, who tells them she is aware of mysterious activities going on at the neighbor's house and has telephoned the police. The Kids, in the meantime, have gone to 322 Elm, and thinking that it is Jack and Betty's new house, borrow furniture from the unoccupied house next door, 321 Elm. They soon get spooked, however, when a disembodied voice laughs and talks to them throughout the house. Unknown to the boys, the ghosts are actually a Nazi subversive group comprised of leader Emil, Bruno, Monk and Hilda, who operate in secret passageways. The Kids run into the cellar and there discover a printing press and Nazi pamphlets. Still believing that the house belongs to Jack, they move the press to 321 Elm, hoping to save him from possible arrest. Jack and Betty forego their honeymoon and arrive home just after the police approach their house. When the Kids realize their mistake, they move the printing press back to 322 Elm, but the Nazi group returns it to Jack's house. After a chase in and out of the secret passageways, Mugs and Glimpy are captured by the Nazis, only to be freed by the rest of the gang. The Nazi gang is captured and arrested. Later, Glimpy, beset by German measles, is quarantined with the Kids at Betty and Jack's house, and the newlyweds bemoan their thwarted honeymoon.