The whole idea of holistic detecting works against any conventional idea of plot. After all, if everything is connected, if the universe really is a mass of tangled coincidences, then order and reason doesn't matter at all. But hey, it doesn't matter as long as it's funny.

And it mostly is funny. Adams has a beautiful way of describing the friction of England: the impossibility of getting a pizza to go or a packet of cigarettes, mono-maniacal psychiatrists, traffic in London, hygiene chicken over a refrigerator. He also has an eye for the absurd. Dirk Gently's arrival at the murder scene of his former client, with a severed head on a turn table, is quite moving (don't pick it up, don't pick it up, don't pick it up). Likewise, the whole sequence with him getting attacked in his apartment by an eagle is also hilarious.

But the overall plot, about Norse gods, conflict between Odin and Thor, corporate types signing contracts for divine power, and so on, just sort of sit there. It's funny, but not that funny.