Paul Foster is apprehensive about the idea, forced on SHADO by the Pentagon, and sure enough, two days later Space Scout encounters a UFO. Pursuing it into space outside its operational area, the ship is surrounded by UFOs, and the crew quickly overcome. Two Aliens pilot Space Scout back to Moonbase, and are able to gain control by overpowering Paul Foster. When contact with SHADO Headquarters is restored, Foster uses names of operatives as a code to warn Straker Aliens are in control. As a UFO armada orbits Earth, the Alien commander on Moonbase takes Foster to his UFO, but he makes a break for Space Scout. With a UFO in pursuit, Foster pilots the ship back to Earth. Sky One destroys the UFO, and Foster reports to Straker. The UFOs start their attack, but Pentagon forces are waiting and drive off the offensive. The Alien commander tries to destroy Moonbase in retaliation, but is also killed by SHADO operatives..