The thing that everyone knows about Magnus Mills is that he used to be a bus driver. Actually, for all I know, he still is. Until now, though, he has resisted writing about his most famous occupation. Why the change of heart? "I think I just decided it was time to explain," as Mills put it in an interview (whose headline, rather wittily, was "Back to his routes"). And we can be very pleased he has done so. Opinion is divided about his recent novels, but pretty much undivided about his Booker-shortlisted first, The Restraint of Beasts; its deadpan humour, coy flirtation with allegory, and menacing air were the kinds of things that the Standard British Novel simply didn't do; there was something central European  Czech, mainly  about it. (And all the more welcome for that.)

If you think Mills's form deserted him after that, this is a return to it (I am not so sure it ever went away). It really is quite wonderful, as if Franz Kafka had been conscripted to write an innuendo-free episode of On the Buses (surely I can't be the first to have come up with that formula). As it is, while notionally set in an unnamed Everycity, it could only have come from this country and, from the odd fairly easy clue, London. As one of the book's increasingly mad and hilarious conversations puts it:

"Funny, isn't it? I can't imagine them having buses in other countries. Only this one."

"Well, I can assure you there are buses on all five continents," said Edward. "I should know. I've studied them."

"When?"

"During my holidays."

(Thus the ghost of the phrase "busman's holiday" hovers self-effacingly in the background.)

Mills always lets us catch something out of the corner of our eye, or makes us wonder whether we have or not. Here it is religion, although the most ostensible target of satire is bureaucratic dogmatism: the strict maintenance of headway, or the gaps between buses. As anyone who has ever taken a bus knows, they come, annoyingly, in clumps (or, depending on your point of view, a "convoy" of buses, or a "liberty of buses". "When all the buses fly past without stopping it's a 'skein of buses'; and then, of course, there's the most prevalent form of all, namely a 'dearth of buses', which is self-explanatory." Isn't "skein of buses" marvellous?). The Maintenance of Headway explains why, and also why all attempts to eradicate the problem are doomed to failure.

This is very funny, and the insider knowledge Mills brings to this subject, which is not in the slightest bit trivial, only makes the eschatological echoes more tantalising. Buses are about transporting human souls and, as fallen creatures, nothing can be done to make them any better; and the drivers' remarks about passengers (usually called "people" once they are on the bus, as in "what have you done with your people?", said by an inspector to a driver who has had to stop his bus because its windscreen wipers have failed) show various shades of indifference, as angels might speak of us. Not that they can ever be actively malicious: there is the unspoken crime, the dreadful example of Thompson, the only driver they know ever to have been sacked. (You'll find out why.)

If we want to insist on its allegorical nature (there are plenty of invitations to do so, with words such as "heresy" and "prophesying" popping up, and the searching question "do you believe in the maintenance of headway . . . truly believe?"), this is very much a gnostic work, with the Board of Transport a fallible, incompetent, culpable demiurge. On the rumour that inspectors are to be replaced by satellite surveillance: "You're joking. The Board of Transport couldn't launch a frying pan into space, let alone a satellite."

But this is Mills having his little joke with us. And yet one has every reason to believe that this is an utterly realistic portrayal of the routine of running a bus garage, exploiting all the fond associations, exasperated or not, this nation has towards its bus system.