The story is set in London, Las Vegas, the Channel Island of Jersey and on the paradise planet Carillon. The 4th Doctor is dropped off for a stay in London in December 1968 by Romana, who leaves for Carillon, where she meets a Time Lord called Nostradamus. Whilst the two of them are having dinner, they are attacked by servants of The Reaper, the story's titular evil entity from beyond this plane of existence. Meanwhile the Doctor, assisted by a certain singer, is engaged in a round-the-world quest to save his friend, Professor Dural, becoming part of the battle to defeat the Reaper.
- The narrative contains a few not-too-subtle references to real-life 20th century icons – there is a chance (but highly useful) meeting with a very upper-class lady walking her small dogs near Buckingham Palace, and when the Doctor visits Vegas, he bumps into some chap called Armstrong who is shortly to have the Moon play a significant part in his future; he subsequently meets an unnamed, leather-clad, sideburned American singer of rock'n'roll, who's just come from a highly successful gig, and drags him along for the remainder of the action.
- According to the closing line of the story, the latter figure is later taken from Earth by the Doctor, on 16th August 1977, to retirement on Carillon.
- The planet's name has nothing to do with the small press 'zine, Carillon, which was founded a couple of years later than the publication of this story.
- Elements of the story appear in The Harvest of the Corn.