Dirk Gently, who calls himself a "holistic detective", has happened upon what he thinks is a rather comfortable situation. A wealthy man in the record industry has retained him, spinning a story about being stalked by a seven-foot-tall, green-eyed, scythe-wielding monster. Dirk pretends to understand the man's ravings involving potatoes and a contract signed in blood coming due; when in reality, Dirk is musing about what he might do if he actually receives payment for his "services" – such as getting rid of his refrigerator, which is so filthy inside that it has become the centrepiece of a showdown between himself and his cleaning woman. The seriousness of his client's claims becomes clear when Dirk arrives several hours late for an appointment to find a swarm of police around his client's estate. The aforementioned client is found in a sealed and heavily barricaded room, his head neatly removed several feet from his body and rotating on a turntable. While at his recently deceased client's house, he discovers that his client had a son. However, after Dirk disconnects the television set the boy had been watching, the boy promptly breaks Dirk's nose.
Nearly incapacitated by guilt, Dirk resolves to take his now-late client's wild claims seriously. During his investigation, Gently encounters exploding airport check-in counters, the gods of Norse mythology, insulting horoscopes, a sinister nursing home, a rhinophagiceagle, an I Chingcalculator (to which everything calculated above the value of 4 is apparently 'a suffusion of yellow'), an omnipotent being who gives his powers to a lawyer and an advertising executive in exchange for clean linen, and an attractive American woman who gets angry when she can't get pizzadelivered in London.
The central premise of the book is that gods are created by humans' necessity and desire for them, and, once worshipped by man, don't disappear but remain on earth forever. Because nobody worships them, many become destitute, like the tramps whom Dirk witnesses entering Valhalla.
Odin makes Thor accidentally transmogrify objects when he gets angry, in a bid to delay him getting to Norway and finding the Draycotts' contract.
The eagle that pursues Dirk and Thor is the transformed jet fighter that tries to stop him from getting to Norway. Thor's inability to fly to Norway using his hammer is why he needs to visit the airport at the opening of the novel.
Odin makes contact with the Draycotts after seeing one of Cynthia Draycott's adverts for a soft drink, which seemingly involve various gods promoting the drink; one of these adverts is seen when Dirk confronts Anstey's son early in the book.
Odin, like all the gods, is naive and quite literally unworldly; this is how the Draycotts are able to take advantage of him.
One of Dirk's chief characteristics in the novel is guilt—about the fridge and about the death of Anstey, whom he should have protected. At the end of the novel, Dirk's fridge generates a new god of Guilt.