Saw

Two strangers wake up chained in opposite corners of a grim, tiled bathroom with no memory of how they got there. It quickly becomes clear that whoever put them there has left them a very specific, and very cruel, set of rules to follow, and no interest at all in explaining why.

The fear here isn't jump scares waiting round a corner, it's the slow, sick dread of watching a situation get worse and worse with no way out. It gets under your skin rather than making you leap off the sofa, though there's blood enough to make you wince into a cushion more than once.

This is one for the night you want your horror properly nasty rather than atmospheric, ideally with the lights on and nothing sharp within reach. Save it for when you're in the mood to be genuinely unsettled rather than just mildly spooked, and maybe don't watch it over dinner.

It suits anyone who likes their horror with a puzzle at the centre of it, less concerned with monsters than with what people will do to stay alive.