A 12-year-old orphan who has just inherited a fortune is trapped on an island with his uncle, a former British intelligence commander who intends to kill him. A young girl is the boy's only ally against the sarcastic uncle, who uses hypnotism, a pool of sharks, fire, and poisonous mushrooms as weapons.
Following the death of multi-millionaire Russell Harrison in a car crash, his $5 million estate falls to his only child, 12 year old Barnaby Harrison, who will receive the money when reaching his age of majority. In the meantime, Barnaby will live with his uncle, Major Kevin Harrison, who resides...
Following the death of multi-millionaire Russell Harrison in a car crash, his $5 million estate falls to his only child, 12 year old Barnaby Harrison, who will receive the money when reaching his age of majority. In the meantime, Barnaby will live with his uncle, Major Kevin Harrison, who resides on a remote, sparsely populated island eight miles from the mainland. During World War II, Kevin was a James Bond type British Army Intelligence Commando and has published an account of his war exploits entitled Killing the Enemy, detailing his multiple accounts of extreme close combat killing of various Germans.
Barnaby is escorted by Police Detective Sergeant Frank Travis on a cruise to the island. Aboard the boat is Chrissie, who is Barnaby's age. The two children constantly argue, with Chrissie believing Barnaby is telling fantastic lies about his uncle's exploits, though Frank does reveal himself as a policeman to her. Chrissie has come from a broken home and will be living with her Aunt Justine, who lives on Uncle Kevin's island.
Barnaby's bad behavior continues on the island, with Frank chastising him for playing with his detective revolver, Barnaby leading Christine astray by visiting a dangerous decrepit hotel and Barnaby keeping up a constant litany of tall tales to impress or frighten Chrissie. Barnaby, however, worships his heroic Uncle Kevin and enjoys reading his book. One night, Uncle Kevin, dressed in his wartime military beret and battledress (as he does on the cover of his book), visits a sleeping Barnaby and wakes him to go on an adventure with him. Leading Barnaby to high cliffs overlooking the crashing surf, Uncle Kevin hypnotizes Barnaby to walk in specific directions with the aim of having Barnaby fall off the cliff to his death, whilst Kevin is home in his bed. The next day, Justine sees Barnaby perilously close to the edge of a high cliff and shouts at him, waking him out of his trance.
A shaken Barnaby believes that he was walking in his sleep until Uncle Kevin later jovially explains that he intends to kill Barnaby for his inheritance. Though his first attempt at eliminating him in a manner appearing accidental failed, he vows to try again. Kevin also explains that his home is "Switzerland", an area of neutrality where he will not harm Barnaby, and adds that he will also not harm Barnaby when he is with Justine or Sgt. Travis, the latter of whom still remains on the island as Uncle Kevin's guest.
Based on Barnaby's previous lies and hysterical behavior, no one believes him, until Chrissie discovers the truth and gleefully suggests they kill Uncle Kevin first. The trio begin a series of cat and mouse assassination attempts against each other. When Uncle Kevin discovers that Chrissie stole Sgt Travis's revolver and came up with an unsuccessful assassination attempt, Kevin includes her in his game.
