Every Friday our film critic Grace Kinsey reviews a new release at the cinema. This week she gives her verdict on Split starring James McAvoy.

M.Night Shyamalan's latest horror revolves around Kevin Wendell Crumb (James McAvoy), who as a child was a victim of abuse, and who as an adult suffers a severe case of Dissociative Identity Disorder (DID), which causes him to house 23 different people in his body .

Psychiatric patients have long been a point of fascination for directors and cinema-goers alike. However, whereas many psychological thrillers create horror out of a disorder itself, Split merely uses DID as the premise for the horror that ensues. It sets the scene for a series of unsettling events and for the development of several individually troubling characters.

And because the film's aim is not to explain DID or portray it as something terrifying in its own right, it does not seem to matter that Split's climax involves a purely fictional symptom of the illness, nor that even the film's psychiatric discourse is sensationalist. This sensationalism absolves the film of any responsibility to do DID justice, and importantly, increases the film's scare-factor.

Thanks to DID as a premise, James McAvoy really has an opportunity to show the audience what he is capable of. In total he is credited with eight roles, and he plays them all seamlessly. Not only is he convincing as one person who embodies 23 others, he is believable as every single one of those others, from the nasty matron-esque Miss Patricia, to Barry the camp fashion designer.

A scene where 'Hedwig', a nine-year-old who inhabits Kevin's body, moves erratically and violently to a dance track shows McAvoy in a particularly chilling performance. The creepy nature of this scene is emphasised by claustrophobic camerawork, trapping the audience in the windowless room with the frantic Hedwig and his deafening music. Furthermore, the head-on filming, and McAvoy's eye contact with the camera, gives the impression that the audience is watching him from behind a double-sided mirror. This plays on the idea of multiple people inside one body: when you look in the mirror, you see one person. Yourself. But what if 'yourself' were actually made up of many people? When Hedwig dances in front of a double-sided mirror, he sees one physical being, but behind that there are many individuals, namely the audience. And this represents Kevin's state of mind.

Shyamalan's Split is among the scarier thrillers I have seen recently, thanks to a remarkable performance from James McAvoy, and the director's twist on a common theme.