Based on stories by Carolyn Keene, two teenagers find a kidnapped woman.
At a girls school Mary Eldredge (Helena Phillips Evans) donates $250,000. Hollister (Charles Trowbridge) tells Nancy Drew (Bonita Granville) and her father Carson Drew (John Litel) that Mary Eldredge is gone. Nancy says that she will find her. Nancy sees a suspicious car but gets a flat. Dr. Ray Spires tells Carson and Nancy that he was abducted to treat a lady and asks them to tell the police. Two men follow them. Nancy and her friend Ted Nickerson (Frankie Thomas) learn of a carrier pigeon from Spuds, and Nancy finds the password "bluebells" that Dr. Spires heard. Her father shows Nancy the news that Dr. Spires was nearly beaten to death. He tells her to take the pigeon to Captain Tweedy (Frank Orth); but it escapes, and she and Ted drive after it to a house. Nancy calls her father, who brings the police. Captain Tweedy storms the house and finds Hollister, who shows them pigeons. Captain Tweedy ridicules Nancy. Hollister sends a note by pigeon. When Challon (James Stephenson) gets the message, he sends a man against the Drews.
Nancy visits Dr. Spires and learns about a bridge and gravel. Nancy and Ted attack a man outside her house, but it is her father. They find the door blockaded, and maid Effie says a man tried to get in. The man appears with a gun and warns them. Carson says they are leaving town, and the man leaves. Carson tells Nancy that Mary is in St. Louis. Nancy goes with Ted to the lake, where she sees Hollister and realizes he lied. They rent a plane and photograph the place. They drive there, and Ted keeps Nancy off the electric fence. Disguised as a widow and a nurse they drive in by using the password. Nancy finds Mary and helps her escape. A man sees that Ted is not a nurse; but Ted knocks him down. Their car is stopped, and Challon has Nancy and Ted locked in the cellar, where Ted finds an x-ray machine. Hollister tells Challon he is going to the police but is knocked out. Ted disrupts radio signals and sends code. Carson tells Captain Tweedy that Hollister is trying to get money. Captain Tweedy gets Ted's message, and they rush to the house. Ted knocks away the gun, and Nancy gets it. Police and Carson rescue Nancy and Ted. In the final scene Mary thanks Captain Tweedy and gives the credit to Nancy.
This detective story with young heroes was so popular that other Nancy Drew movies soon followed, indicating the trend for movies about teen-agers, who are smart and full of energy and initiative. In this mystery they save an elderly lady from being exploited for her wealth by being imprisoned in a sanitarium.