"Everything is permissible if God does not exist," wrote Jean Paul Sartre, "and as a result, man is forlorn because neither within him nor without does he find anything to cling to."

Within the wide-ranging 20th-century canon of existentialism, Albert Camus explored his own doctrine of alienation and the 'absurd', most famously in his novel The Outsider, his essay on The Myth of Sisyphus and in this, Caligula, his play about the blood-obsessed Roman emperor. His damning verdict on life's only real truth is summed up in the words of Caligula: "we die and we are unhappy".

So, even if the play's title doesn't conjure up pornographic images of Malcolm McDowell from Gore Vidal's infamous 1979 screen version, it's little surprise that it makes for distinctly uncomfortable viewing. In fact, Michael Grandage's superb production, of David Greig's fluid new translation, makes for one of the most disturbing - and yet utterly compelling - evenings I've spent in the theatre.

After the premature death of his incestuously beloved sister, Caligula, driven by his loss of love and faith, returns from three days of wandering introspection to pursue his right to "absolute freedom" in absolute power and to share "the gift of meaningless" with his kingdom via random executions, calculated famines, blasphemy and bloodlust.

In the title role, Michael Sheen, making an overdue return to the stage, is nothing short of mesmerising. He terrifyingly captures Caligula's frenzied, sleep-deprived insanity and the mercurial nature of his cruelty, never more so than when pouncing on a quaking old man to force-feed him poison. And, in his flickering moments of doubt and guilt when Sheen delves into his despair, you feel plunged into the deep lake of darkness with him, the metallic taste of guilt and fear on your tongue. It feels difficult to breathe.

In supporting roles, Raymond Coulthard provides Sheen's Caligula with a dispassionate philosophical foil as Cherea, while Diana Kent and Jason Hughes add to the fright factor as the loyal ex-mistress and servant who become his apologist acolytes in viciousness. Caught in the muddled but moral middle is Ben Turner's poetic Scipio, while the assembled patricians ably register the strains of their emperor's reign of terror.

Adding to the production's psychological tension are eerie murmurings, brutal beatings and heightened music (care of Fergus O'Hare and Adam Cork); the stage left largely blank to be overrun with the conflict of characters and ideas.

Though existentialism itself may have fallen from fashion, Camus' play has tapped once again into timeliness. When it premiered in 1944, Hitler's horrors were still fresh. Now, we have our own tyrants with whom to draw uneasy parallels. And, in Grandage's production, we have one of the most arresting and gruesome closing images, a bloodied Sheen, smeared against the silvered brick backwall, plaintively lamenting his life.

Shocking, spine-tingling - and yes, stomach-churning - stuff.

- Terri Paddock

To read our 20 Questions interview with Michael Sheen, click here.