It was possibly the kindest, most humane invasion ever. Nobody was killed. Nobody was even bruised by it. At least, not at first.

Three landings, three countries. Brigadier Lethbridge-Stewart soon realises this is too big for the Fifth Operational Corps, and so plans are put into place for an international operation, with Bill Bishop and Anne Travers sent to the US to work alongside Colonel Hickenlooper, Colonel Douglas goes to the USSR to liaise with Major Bugayev, and Lethbridge-Stewart is joined in the UK by an old American ally from his National Service Days.

Just what is going on, who are the Engineers, and why do they insist they have an agreement with the King of Earth? Lethbridge-Stewart finds himself having to deal with international politics and inter-galactic agreements, while Anne has to cope with a Russian spy, and a trip to an alien world…