The Assassins' Guild is a society at Cambridge University that runs a variety of the game known as Killer, which was at one point published in a book by Steve Jackson Games.
The object of the game is to track down and eliminate the other players, while also staying alive yourself. “Assassination” is carried out with a variety of harmless toys or fake weapons which range from pens labelled as ‘knife’ to water pistols and the popular Nerf weaponry. Often people come up with more inventive and amusing ways to dispatch their targets.
To find out more, I suggest you read the reports of past games available in the archives, and read the current game rules. If you are in Cambridge and would like to get involved, or would like any more information, then please email assassins@srcf.ucam.org.