Computer adventure games, as difficult and as complex as they can sometimes be, are a one-way process. It's you versus the machine. Add a few more players and things become more interesting and challenging.

And that's the attraction behind multi-user games, of which Shades is the latest example. It's the brainchild of Neil Newell and is currently accessible to subscribers of Micronet 800 and Prestel.

The key to it is the involvement, the knowledge there are other people out there, waiting to react to your decisions and you to theirs.

As Neil says: "The scenario is really there as a backdrop to provide the vehicle for the development of the player's character."

Character building is all-important, to make progress to the very top of the tree and become Arch Wizard. Play behaviour has to be policed. There is nothing more soul-destroying than constantly being knocked back to the rank of Novice, by some thug intent on trying to kill you every time he comes across you.

So Arch Wizards can cut players out of the game if they become a nuisance to others. "Strangely enough, one of our biggest all-time killers was a surgeon in real life!"

Swearing, too, can get you banned. Utter an obscenity when an Arch Wiz is around, and you may be out with no warning.

"The last time we arranged to meet in the bar of a London pub," says Neil. "Seventy people turned up."

Seventy people took the trouble, eh? Sounds as if something interesting is going on here - let's enter the gateway, and see what gives...

Shades is a multi-user adventure, available to anyone with access to Prestel, or preferably to Micronet, through your computer. This means that you need a modem, some communications software, a suitable telephone point and a subscription. The subscription to Micronet is payable on top of the basic Prestel subscription, but once a subscriber, playing Shades becomes much cheaper.

A multi-user adventure is fundamentally different from a 'normal' adventure played on a standalone computer. It is played in 'real time' (more on the frustrations of that later!), and there is no way of 'completing' it.

Points are gained by collecting treasures, and depositing them in the Mad King's Room in the castle - one of the locations in the castle area of Shades.

Additional points can be won by killing 'mobiles' (independent computer-generated characters) and other players in the game, although this latter course of action is frowned on somewhat, and too much of it can result in disciplinary action by a Wizard.

Up to eight players can populate a game, and there are a number of games running simultaneously to ensure that anyone who wants to should be able to find a vacant slot.

If killed, points are lost, and the player gets knocked out of the game, having to re-select one of the games in progress to continue playing.

In the normal course of events, all the treasures would be gobbled up and lost forever. To overcome this, every so often there is a 'game reset', when everything starts from scratch, and the players have to link in to one of the games again.

There are puzzlers, but of course, once solved they can be romped through quickly during the many inevitable replays. The thing to do seems to be to find a game that has just started, and rush to where you know the treasure is, grabbing as much as you can before the other players get there.

There are effectively more than 760 locations in Shades, and they are being changed and added to all the time.

It is all great fun - more a way of life, perhaps, than an adventure game. Provided you can afford the phone bill, plus nearly £1 per hour (There are connect-time charges during the daytime on weekdays, as well) then it's worth taking the risk that you won't become totally addicted to it.