Axel Nordstrom manages a
glass-bottom boat tourist operation on
Santa Catalina Island, California. His widowed daughter, Jennifer Nelson, helps by donning a mermaid costume and swimming underneath his boat for the passengers' amusement. Jennifer meets Bruce Templeton when his fishing hook accidentally snags her costume. He reels in the bottom half, leaving Jennifer floating in the water
bottomless. She later has a run-in with Bruce at her new place of employment, an
aerospace research company in
Long Beach, where she works in public relations. Bruce's company created GISMO ("Gravity Inertial Stabilized Manned Observatory"), a gravitation control device which the
U.S. Air Force plans to put into orbit in weeks and whose secret formula is sought after by the
Soviet Union. Bruce hires Jennifer to write his biography, while he works on GISMO. At his home, she meets electronics technician Julius Pritter and Edgar Hill, a
CIA agent ensuring the GISMO project is securely handled. When left alone in a room, Julius starts searching for information regarding GISMO. He photographs a cryptic note written by Bruce while brainstorming ideas about how to win Jennifer's affection. Julius transfers the photos to his handler. Bruce drives Jennifer to Catalina. His remote-controlled boat malfunctions, throwing Bruce out and landing in a parking lot with Jennifer. Bruce and Jennifer later spend an evening with Axel and his wife. Bruce is summoned to a meeting with Hill, security guard Homer Cripps, and PR executive Zack Molloy. Hill reveals that secret information is leaking, such as the note that Julius photographed. Cripps is suspicious of Jennifer because of things he noticed about her: She repeatedly calls the same number every day, counts the rings, and then hangs up with the words "that's all for now, Vladimir"; she burns papers alone at night in the office; and she has a shortwave antenna installed in her home. There are innocent explanations for all of these things, which none of the people there know about: Vladimir is her dog, who gets his exercise by running through the house barking whenever he hears the phone ring; Jennifer read a note in the office explaining that old documents should be burned so that they cannot be stolen; and she uses her shortwave antenna to communicate with Axel. Bruce begins to suspect that Jennifer is a spy. Air Force General Wallace Bleecker later arrives to watch over the GISMO project. Julius is confronted by his handler for only providing useless or publicly known information and is pressured into spying at a party which Bruce will host the next day. Cripps, meanwhile, spies on Jennifer, overhearing her talking to Axel and misunderstanding her end of the conversation as further proof of her involvement in espionage. At the party, Jennifer declares her love for Bruce. They plan to spend the night together, but Bruce is again called away to a meeting with Hill, Cripps, Molloy, and Bleecker. While picking up the phone to call Vladimir again, she overhears their discussion and learns that they suspect her of wrongdoing. Bruce defends her and believes in her innocence, remarking that she is not intelligent enough to be a spy. Furious, Jennifer starts pretending to be a spy. She arranges for Molloy and Bleecker to have an embarrassing
tête-à-tête by promising to meet both at the same time in the guest room. She ties up Cripps, when she sees him tailing her. After noticing Jennifer's deeds, Bruce becomes angry and locks her up in the closet. She is freed by a hidden Hill, who actually is a spy. He stole the formula and placed it in Jennifer's purse to smuggle it out of the house. Returning home, Jennifer is confronted by Julius. Hill then arrives, draws a gun, and demands the formula. Julius and Jennifer fight him off, and she flees while Bruce, Cripps, Bleecker, and Molloy, who realized the truth, race to save her. Hill is stopped by a blow with a bedside lamp by neighbor Mabel Fenimore. Jennifer and Bruce later have a honeymoon and ride the boat, which again malfunctions and leaves them in the parking lot on Catalina. ==Cast==