SHADO engages in its first battle with the enemy. Sky One cripples an alien ship which crash-lands in a lake. Straker's team capture its pilot, a strange blue-skinned humanoid - and the grim secret behind the aliens' are revealed.

After a pilot is killed when Moonbase operatives fail to give him course change information, the personnel are recalled to Earth for an investigation. A UFO crashes in northern Canada and the personnel are assigned to the operation to find the UFO. Gay Ellis is to coordinate the movement of the mobiles trying to approach the UFO.