A pair of musicians are performing their act when one of them is almost electrocuted. Mannix is hired to look into the matter. But the detective faces twists almost immediately. For starters, the woman who hired Mannix isn't who she said she was. Mannix also needs to act fast before another attempt on the musician's life is made.
At the start of a long weekend, off to a fishing vacation with friend Tony Elliott, Mannix stops at Tonys office so Tony can pick up a set of fishing flies. They walk in on a methodical heist of the businesses in the building. Mannix is trapped in the building, playing a cat and mouse game with the three burglars.
Mannix travels to an island that's part of a South American country. Mannix's client wants to repay the man for the saving the life of the son of the client some years earlier. But Mannix soon discovers the case is more complicated than he bargained for. The man he's searching for is part of a plot to assassinate the president of the country. Just as Mannix is putting the pieces together, he's captured by the conspirators.
The conspirators assassinate the president of a South American country and successfully frame Mannix for the killing. Now, the detective must dodge the authorities and hunt the conspirators as he tries to clear his name.