PEOPLE are always complaining that the digital world of gaming, Facebook, instant messaging and illegal downloads are ruining kids and taking over the arts.

As the mother of a 17-year-old son who appears to be physically attached to his computer, I couldn't agree more. So when I was sent Covenant by Mel Odom to review I got a little hot under the collar.

Covenant isn't just a book about demons invading the world and humanity being defended by modern-day Templar knights with high-tech armour and 'spike-bolter' guns. Covenant is actually based on a computer game!

Yes. Gaming has taken over that last bastion of culture, literature.

What surprised me even more though, much as I hate to admit it, is that it's actually quite good. In fact, Covenant is a rollicking action read with strong characters, an interesting plot and lots of monsters to be destroyed.

Based on the video game Hellgate, Covenant is one of a series of books that have been published as a stand-alone companion to the game. You don't have to have played the game to read the book, nor vise versa.

The author Mel Odom is actually well-known for writing expanded storylines in the 'alternate universes' of gaming, TV and movies. He's written tie-ins for Buffy the Vampire Slayer and Blade for example.

So, Odom knows how to write action, he is a dab hand at unlikely senarios, and yet he's also able to add that jolt of humour and humanity that makes okay speculative fiction into great speculative fiction.

Covenant follows the trials and tribulations of three groups of humans fighting against demons who have erupted through some sort of 'rift' from another universe into the city of London.

The Templars are the modern-day version of the knights of old.  They fight for the innocent wearing armour and using broadswords – only now they have nano-techonology that can create extra-strong, extra-powerful guns, grenades and swords that can shear through a demon's tough hide. The Templars are also beset by ancient traditions of chivalry and upper-class in-fighting but at least one of them, Simon Cross, is out to save the world.

The Cabalists are a group of humans who generally believed in magic, spiritualism and things-that-go-bump before the demons arrived and are now over-joyed (in a way) that they've been proven right in their beliefs. However, they've gone a little too far and have a tendency to graft bits of demons onto their bodies – yep, they've got horns and armour and even tails stitched onto them.

Warren is kind of a cabalist – he had an innate ability to manipulate people that's become stronger the longer he spends time with the demons. Although he works for the demons, he's not really happy about it, but is more concerned with staying alive than trying to save anyone else.

The third group is a mysterious government organisation – MI5 maybe? - that is trying to at least delay the demons from taking over the rest of the world. They're very secretive, have some technology – which appears to have been stolen from the Templars – and may have another agenda entirely.

In the Covenant, it works out that all three groups must somehow come together in order to save the world from the demons – although this isn't likely to happen as none of them trust each other.

There's also a love interest with Simon having an bit of thing for Leah who works for the mysterious government organisation; and Warren does have at least one human who he seems to care about.

So, despite the fact that Covenant is based on a computer game that I wouldn't be caught playing; this is actually a jolly good read. The prose is tight, the characters are oddly realistic and the premise holds together well with actual historic information and religious legends giving the story depth.

In fact, the only off-putting thing about reading Covenant, for lovers of speculative fiction anyway, is the cheesy link to the video game slap-bang on the cover.

Mind you, the link to the video game did win me Brownie points with my son – who, like most teenagers, believes all parents are dinosaurs. So, maybe I've got something to thank Hellgate for, after all.

Covenant by Mel Odom is published by Gollancz and is available from good book stores and online.