Responding to a strangely worded advertisement, Captain Mike Yates (retired) is reunited with a ghost from the past. But why has the Doctor, that mysterious traveler in time and space, sent for his former UNIT acquaintance? Beset by vicious creatures in an English country cottage, the Doctor tells Mike about his recent adventures, travelling through the Centuries right back to the Middle Ages. In each location he battled a powerful race of alien insects intent on global domination. But now they are here, in the 21st Century--and it's up to the Doctor and Mike to defeat them.