Making a successful film about mental illness seems like a tricky challenge, but props to director M. Night Shyamalan for pulling off such a spectacularly eye-opening, scary yet brilliant film.

We meet Kevin (James McAvoy) who has dissociative identity disorder (DID), meaning he has 23 different identities, ranging from a Kanye West loving nine-year-old named Hedwig to a prim and proper English lady named Miss Patricia.

But, when we first meet him, he is an odd, revenge-filled, neat-freak called Dennis who abducts three teenage girls and hides them in a maze-like, under-ground lair (which is ironically quite dirty).

The outsider of the three girls, Cassie Cooke, played by Anna Taylor-Joy, sees an opportunity to manipulate the immaturity of Hedwig and asks to help him the girls get free, much to the dismay of Cassie when she realises the ‘window’ in his room is merely a drawing.

Another one of Kevin’s identities, Barry (a fabulous, fashion-savvy designer from Brooklyn) meets with their therapist who fully supports individuals with DID and naively believes they are capable of super-human abilities – a hypothesis which is later answered.

A re-occurring nightmare for Kevin’s identities is ‘The Beast’ which the traumatised teenagers are warned about. However, it is later shrugged off by the teenagers and the therapist on a number of occasions suggesting it is not real.

McAvoy’s performance is undoubtedly phenomenal, switching from one identity to another within a matter of seconds, all completely convincing and scarily realistic.

This film explores the sensitive subject of mental illness, whilst thoroughly entertaining the audience with wit and a vast array of twists, turns and traditional thriller characteristics of a truly incredible film.