In New York's Lower East Side, young Tommy Woodry [Bobby Driscoll] has a habit of crying wolf. Late one night, while trying to sleep on the building fire escape, he glimpses his two seemingly ordinary neighbors, Joe Kellerson [Paul Stewart] and Jean Kellerson [Ruth Roman], murder a drunken sailor inside their apartment. Tommy's story meets a cold wall: neither his parents nor the police believe him, chalking it up to one of the boy's tall tales that never quite add up.
Mary Woodry [Barbara Hale], the boy's mother, tries to coax Tommy into apologizing to the Kellersons, hoping to keep the peace, but the boy refuses, and suspicion surrounds him. With Ed Woodry [Arthur Kennedy], the father, away at his night job and Mary busy caring for a sick relative, the Kellersons decide to act on their fear that Tommy will expose them. They lure the boy under the pretense of going to the police, guiding him into a dark alley where they attempt to end him.
Tommy manages to slip away, but the Kellersons quickly recapture him and haul him back to their apartment in a taxi. He cries out for help, yet a passing officer hesitates, recalling the earlier visit to the station and not fully trusting the boy's claims. The Kellersons cunningly pose as Tommy's parents, fooling the cab driver and complicating any chance of rescue.
Back at home, Ed Woodry returns to an empty apartment and enlists a nearby police officer to search for his missing son. The chase spills into the streets and onto rooftops as Tommy dashes from danger, with the Kellersons in close pursuit toward a building that is already being demolished. The officer pieces together that Tommy may be seeking his mother, and Woodry and the officer move away from the peril, hoping the trail cools.
On the roof, the pursuit becomes a perilous game of balance. Tommy discovers the murdered sailor’s body and pushes upward, with Kellerson closing in. The stairwell buckles, leaving Kellerson gripping a shaky beam while Tommy clings to the narrow support above the void. Neighbors rally with a rescue net, ready to catch him if the beam collapses.
In the tense moment that follows, Tommy directs the rescuers to the crime scene and to the whereabouts of Mrs. Kellerson, and the murdered man’s body is finally found. The beam gives way, but the net catches him just in time. As Tommy is led to a police cruiser for safety, his father expresses pride, and the boy, thoroughly shaken, promises to stop inventing stories once and for all.
