Foucaults Pendulum - Umberto Eco, Vintage Publishing

Three book editors, jaded by reading far too many crackpot manuscripts on the mystic and the occult, are inspired by an extraordinary conspiracy story told to them by a strange colonel to have some fun. They start feeding random bits of information into a powerful computer capable of inventing connections between the entries, thinking they are creating nothing more than an amusing game, but then their game starts to take over, the deaths start mounting, and they are forced into a frantic search for the truth