In 2003 Oxford University philosophy professor Nick Bostrom published The Simulation Argument. This states that "at least one of the following propositions is true": "The chances that a species at our current level of development can avoid going extinct before becoming technologically mature is negligibly small. Almost no technologically mature civilisations are interested in running computer simulations of minds like ours. You are almost certainly in a simulation."

As Ross Baker, the lead character in Christopher Brookmyre's brain-tickling novel, remembers it, this argument "suggested that if the human race survived long enough, in its endeavours to understand itself, it would surely develop 'ancestor simulations': hyper-realistic virtual-reality environments in which the minds inhabiting these worlds were themselves part of the simulation. Such advanced civilisations would  be able to implement billions of ancestor simulations, each containing billions of minds. Therefore, the vast probability would be that you are one of those billions of simulations rather than the single original reality that spawned them."

This argument matters to Ross particularly because his "mind" has somehow been rerouted into a computer game: "specifically, a 1996 first-person shooter called Starfire". He has recently woken up on Graxis, a planet with a sky of regally luxuriant purple where American marines are doing bloody battle with hideous flesh and metal cyborgs. More disconcerting still, he is one of the cyborgs, complete with grafted armour plates and so much wiring and metal on his face that he looks as though he has "faceplanted the clearance sale at Radio Shack".

Ross, a computer programmer who used to play Starfire as a teenager, quickly realises where he's ended up. So he's luckier than Tom, an accountant from Leicester, who is understandably baffled and upset that he has been torn from his family, is being forced to blast space-Yanks with a laser cannon, and can't even escape to death, because he just respawns. In spite of his fondness for games, Ross isn't exactly delighted by his arrival on Graxis either, not least because he's anxious about the pregnant girlfriend he's left behind in what he thinks of as real life. He sets off to find a way home, and soon finds himself battling his way through a geek's paradise of classic games, from 1980s Spectrum favourite Jet Set Willy to more modern multi-million sellers such as Silent Hill  all of which have also been loaded onto the "teetering bank of hard drives" where Ross and Tom and dozens of others like them now seem to live.

Ross's journey into knowledge takes in more Bostrom-inspired philosophy about the nature of existence and ethical considerations about our growing digital heritage, not to mention a few good swipes at corporate greed and predator capitalism. But although this material is stimulating enough, the reason you'll want to keep reading is to get to the bottom of the simulation mystery. Bedlam carries an air of permanent perplexity. Ross quickly becomes adept at "staring blankly like a tit" as he struggles to take in the weirdness of his surroundings and even more adept at having his mind boggled by the implications of his adventures, especially when things start to go wrong in the coding of the game worlds. A less able writer would struggle to control all this puzzlement, but happily Brookmyre (apart from a few occasionally inelegant departures from the game world to describe Ross's "real life" situation) does a fine job of teasing out the strands and keeping an almighty final twist in reserve. There's a gleeful chaos surrounding the variously altered, renewed and collapsing computer-generated landscapes, but the plotting is always tight.

Fans of Brookmyre's previous crime novels will recognise the skill with which he works towards this satisfying revelation. They'll also recognise jokes like this: "Ross couldn't have felt like more of a dick if he had been gene-spliced with George Osborne and dressed in a six-foot foam rubber penis costume." There's a vein of sweary political humour that at its best invites comparison to a younger, edgier Terry Pratchett. Brookmyre also shares the older writer's delight in creating strange worlds with strange physics  and using those rules to wreak havoc in his characters' lives.

And that is a departure. He has written about obsessive gaming before in A Big Boy Did It And Ran Away, but this is his first speculative fiction novel. He changed genre, appropriately, thanks to a video game company. Nick Witcher, a director at RedBedlam and a fan of Brookmyre, wrote to the author asking if he'd ever thought about scripting computer games. Their subsequent correspondence resulted in a treatment for a game currently in production (scheduled for release early next year) and inspired this novel.

So, in a way, Bedlam is that dreaded thing, a computer game tie-in  information I've deliberately held back until now, because I didn't want to put you off. For this is not like all those cynical Halo and Assassin's Creed tie-ins. It is a genuinely engrossing, amusing and intelligent novel. If the accompanying game is anything like as enjoyable, it will be terrifyingly addictive.