App of the Day: Scotland Yard: The Hunt for Mr X

Information asymmetry: when people know things that others don't, and vice-versa. A concept that underpins some of the very best multiplayer experiences, and the foundation of Scotland Yard: The Hunt for Mr X. Set on a large map of London, a team of the noble rozzers have one objective - track down that elusive, tantalising Mr X before he escapes.

The exact size of each game varies, but it's usually four coppers chasing down the villain. Each location in London is joined by transport links, and players move to any connected location on their turn by taxi, bus or tube. Mr X can see the police, and they can't see him. But three times during the game, on the third, eighth and fifteenth turn, his current location is shown.

All that the police have to do is get onto a square occupied by Mr X while he's still there, which results in the arrest and a glowing front page headline. The starting positions are randomised, so the first couple of turns tend to see the police moving towards train or tube stations - after Mr X's location is shown on the third turn, they can then cover a large area of the map quickly to get nearby (taxis and bus rides tend to be much shorter). This preamble always tends to run in the same way, and it's then that the hunt for Mr X really begins.

As well as the infrequent sightings, the police have one other tool. You can see what type of ticket Mr X has used on his previous turns. It's possible to narrow down Mr X's options from looking at these, and begin co-ordinating to tighten the noose around the area where he absolutely must be.

Mr X must rely on invisibility, backtracks and, on one special occasion, a ticket that lets him travel without giving the police any information at all. Because the sightings are so spaced-out, it's possible to entirely wrong-foot every officer on the board with this, sneaking off on a train with the secret ticket and riding around on buses at leisure. By the time the cops get another sighting, you can be so far away they'll take several turns just to get there.

It's slow-motion tag where everything depends on fooling your pursuers (as Mr X) or avoiding red herrings (as the police). Because the information available is so limited, everything depends on the kind of story you tell your pursuers. If they seem to think you're going a particular way, it behooves a decent Mr X to use transport that keeps that illusion intact, even if it means a slower escape. Information asymmetry can be a boon, making your opponents put together the pieces in the way you want.

Scotland Yard's difficult to pin as a particular genre. A multiplayer mystery? Whatever, it's a chase with simple rules set on a board that turns these into complex calculations. You know where Mr X was, and know he took a cab away from it, but which of the two potential routes do you follow? How tight is the noose? It's a game that constantly asks you to make best guesses, decisions made on incomplete information and gut instinct as well as cold calculation. When he gets away, you don't just feel like you've lost. You feel you've been outsmarted.