The Sherlock Holmes marketing machine is looking rather interesting. Already we've seen an interesting piece of press marketing that got sent through to Filmstalker, and now we're seeing something bigger.

For those who solved the first marketing puzzle I talked about and signed up to the site, there's a new online game been released, and this one has a bit of a difference to it. It has to be solved with a partner, your Dr. Watson.

I love this idea, quite frankly it's a bit of genius that really plays to the idea of the story of Sherlock Holmes. The marketing company behind this one should be the one behind most marketing campaigns, for I think it's cracker.

Let me hand it over to the rules of the game over at the official game site for Sherlock Holmes:

221b is a two-player game immersing you into the world of Sherlock Holmes and Dr.John Watson. Launching on October 28th 2009, 221b takes you through the events leading up to the very first scene of the new Sherlock Holmes film.

You can play with a friend, one as Holmes, one as Watson, or you can even play alone if you like, taking on the role of both characters. Just as in the stories, you and your friend will investigate crimes, sift through evidence and solve mysteries. You'll also have to stake your reputation as detectives on your deductions. Get them right and you'll soon be the envy of Scotland Yard.

Let me interrupt the lengthy instructions there and leap in with an exciting trailer to give you something visual to the game. This adds a fair amount to it.

The game is played through an ordinary internet browser, which we recommend setting to full screen(F11 will toggle fullscreen on and off). It's no ordinary web game - as you'll discover when you sign up, it's a rich audiovisual experience. There are two main areas: an interactive window, and a casebook, which stores all the evidence that you discover as you progress.

You'll need a Facebook account to play the game. There is a registration process which uses the Facebook Connect system to link you with a friend, so that you can start playing.

The most important thing you have to do is work together. You can't solve the mysteries unless you and your partner share information and ideas.

Sounds interesting? Well head over to the official site, read all the rules and details of the game, and sign up to play for yourself, but find a friend too, after all you need your Watson.