On Momus, a primitive planet with no mass communications technology, news and information is disseminated by itinerant members of the Newstellers Guild.
One night, a group of travellers sit around a campfire and a Master Newsteller, Boosthit, accompanied by his apprentice, tells a story.
The tale he spins tells of Lord Ashley Allenby, an ambassador from a neighbouring quadrant of inhabited planets, whose mission is to warn the planetary government of an impending invasion.
But the keen listeners around the campfire are one step ahead of the Newsteller, and realise the punchline to be that Allenby is the Master's apprentice.
As Master and apprentice depart, Allenby tentatively suggests improvements to the story to make it more believable.