After "The Sixth Sense" and "Unbreakable", M Night Shyamalan could probably get his tax returns filmed. So it's to his credit that "Signs" finds the Oscar-nominated director taking risks, flirting with new genres and coming up with yet more ways of testing his audience.

Mel Gibson is Graham Hess, a former preacher turned farmer who wakes up one day to find that someone, or something, has carved an intricate pattern of circles and signs into his crops. Turning on the news he discovers that similar symbols are appearing across the globe, prompting fears that the end of the world could be just around the corner.

As if that isn't bad enough, Graham is trying to raise his two young children while coping with a crippling crisis of faith brought about by his wife's death in a car accident. Paranoia and grief make a dangerous combination, and as further unexplained happenings occur, Hess must take extreme measures to protect his family.

To say more would spoil your enjoyment of Shyamalan's chilling psychological thriller, which after a Hitchcockian beginning takes an abrupt detour into science-fiction territory. Suffice to say that the less you know, the more you'll be entertained.

"Signs" is not a total success: there are gaping plot-holes you could drive a tank through, and the goofy humour often undercuts the all-pervasive atmosphere of dread. But Gibson is on top form, and there are some genuinely terrifying moments that will have you cowering behind your popcorn.