The Rangers stop on Mesa to repair Space Tug 4, which was pulling a ship outfitted with an experimental Andorian engine that would render current drives obsolete. A space time distortion opens up, and through it comes a mysterious object, which hits the experimental vessel, and both crash on Mesa. The UFO turns out to be Scarecrow. He takes over a riverboat casino gambler, and teams up with Lazarus Slade. Slade is only interested in getting the new drive, while Scarecrow is after immortality.
