A UFO incident in 1970 triggers a series of secret international meetings. On the way to one of these meetings, a Rolls Royce containing Colonel Straker and General Henderson is attacked by a UFO. Ten years later, SHADO becomes fully operational, with Straker now in command. Colonel Freeman is assigned to pilot an SST containing revolutionary new deep space tracking equipment and its design team. While in flight, a UFO is detected and the Interceptors fail to destroy it. The UFO closes in on the SST, but Sky One is able to intercept it. An Alien occupant survives a crash into the ocean and is taken back to SHADO HQ. What secrets does it reveal?