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.

Foster is suspected of being a security leak, but during the trial, Straker and gang discover that Foster's apartment was bugged and shut down the disreputable business that is selling the spy gear.