The first of the gruesome chiller franchise stars Cary Elwes and Leigh Whannell (who co-wrote the script) as strangers caught up in a deadly game with an unseen serial killer.

They wake up chained to opposite walls of a squalid public toilet. There’s a dead body and a gun in the middle of the room, a saw hidden in a cistern and mystery villain Jigsaw who taunts that one must kill the other to survive…

Meanwhile, detective Danny Glover is trying to track down the maniac in question, while flashbacks (‘There’s only one way to open the device: it’s in the stomach of your dead cellmate!’) flesh out the killer’s ghoulish past.

This bizarre psychological chiller is cruel in the extreme, but also genuinely unnerving and very clever, especially the brilliant closing twist.

The film has spawned eight box-office hit movies so far, as well as a theme park ride.