4.48 Psychosis at the Young Vic

Her eyes flick around the Young Vic's darkened studio theatre, darting towards any noise that emerges from the audience: the sound of someone shifting their weight, a cough, a scratch.

Then, suddenly, she starts to speak. At first the nameless young woman offers her audience brief, disconnected statements. But before long these join together to form the startling and affecting monologue that is "4.48 Psychosis". The play is essentially a free-form poem delivered by an acutely mentally unwell individual who describes 4.48am as "the happy hour when clarity visits".

Anamaria Marinca, the immensely talented actor who single-handedly builds tension and slices through it with the script's gallows humour, cuts a striking figure on the blank wooden set. For the entire 72-minute play her two feet stay nailed to the same spot. Her voice wavers between frustration, fear and weakness. It is an incredibly dynamic performance: in delivering Kane's well-crafted words, Marinca takes her audience on a rollercoaster ride of emotion.

And yet I first felt tedium, thinking that I would not be able to connect with the character, that I could not be anything but a voyeur, observing this young woman's madness without real connection. But gradually I came to know her. I eventually empathised as I recognised the depths and horror of her condition. It is the closest one can get to experiencing mental illness.

But Kane's skill extends further. Not only is she extraordinarily reflective but she also has the guts to thread this into her character, making for crushing tragedy. The character can see exactly what is happening to her, she acknowledges the severity of her illness, but is powerless to stop it. One can only assume that Kane had the same experience, which sets up her other great tragedy: that she hanged herself before the play premiered – and yet it is her finest work.