What would you do if you received a message from an alien superintelligence, via a tray of tzatziki, warning you that the Earth was in grave danger?

Nigel Spleen's life changes when he gets a copy of the game Quincy Moonbeams and the Ululating Tzatziki for his birthday. The next morning he wakes up to yet another day in his disastrous life, but things change when his old friend Duncan turns up, lures him into a VTOL-capable pub and gives him a glass of Bébeme. When Nigel wakes up, they are in the outer thermosphere. Here, Duncan tells Nigel about their mission: a Very Big Thingy is about to crash into the Earth, and the tzatziki overmind has commanded him to team up with Nigel in an attempt to stop it. Nigel is thus forced to address the above question, along with other, more profound, questions that such a situation would naturally give rise to.

On his mission, Nigel, along with the crew of the Septic Carbuncle, journeys to the Large Magellanic Cloud, sits in a bowl of Vaffazzatan Hyperbeetroot stew with an alien who reminds him of a bloke he knows from Solihull, falls through a plot hole, meets someone made entirely from mozzarella, consults The Economist Style Guide to clarify whether 'anteater' is technically a rhyme for 'plant-eater', is ordered to dress someone as a garden gnome and call them Denis Thatcher, fights a Quasivasectomied Querulous Etterkop, listens to the audiobook version of A Concise History of Proctology, briefly becomes half man half tzatziki, solves the mystery of Chekhov's cucumber, learns the truth behind Balzak the Boar—and his alien superweapon the drinking straw of death—and confronts his arch-nemesis the irascible, boorish and supremely abusive Malevolent Taramasalata.