A UFO manages to evade interception by Moonbase and lands on Earth. However, waiting SHADO Mobiles are confused when the UFO only touches down for a matter of seconds before taking off again. But the following morning two scientists are reported as not turning up for work in the same area. Colonel Alec Freeman investigates, only to be ambushed by an Alien in the ruins of Mersham Abbey. Colonel Paul Foster, still in the area in a Mobile, searches for Freeman when he doesn't report in and is also wounded by the Alien. Realising that the disappearances are all connected, Straker lays an ambush for the UFO which will have to arrive to collect the abducted men. Unknown to the commander, a Moonferry has sighted the UFO and intercepted it, causing a delay in its arrival. On Earth, the helmetless Alien is weakening, which gives Freeman a chance to escape, just as the UFO arrives. With no chance of capturing it, Skydiver is alerted and Sky 1 is able to destroy it. WIth a dead Alien and a destroyed UFO, the only positive aspect is that Freeman and the two scientists were not taken.