A fearful, disorientated man, who has (from whose hand we do not know) received a vicious gash across his chest, is ushered by a doctor and a nurse into a huge room in a crumbling Victorian mental institution.

His every move is observed by medical staff, either from the huge-windowed viewing platform above his room, or via the ever- vigilant CCTV cameras that surround him. It is a frighteningly familiar, Orwellian vision.

So opens the National Theatre of Scotland's brave and ambitious one-man Macbeth, in which internationally acclaimed Scottish actor Alan Cumming plays every key character in Shakespeare's great tragedy. From the moment the medics close the security door on Cumming's unfortunate in-patient – with him asking them, "When shall we three meet again?" – the man's mental distress takes him, in the course of a brilliantly sustained hour and 45 minutes, from an appropriately Highland-accented Macbeth, through to a chillingly determined Lady M, a humorously foppish King Duncan, and an agonisingly bereft Macduff.

Cumming has been showered with superlatives throughout his illustrious career, but rarely can he have deserved so many at one time. To tackle this play all but single-handedly might seem like a case of "vaulting ambition" no less perilous than Macbeth's regicide itself. Yet, there are moments when, shifting from one character to another, he gets to the psychological, emotional and erotic heart of the matter with a greater power than many a full-cast production.

Nowhere is this truer than in the pivotal exchange between Macbeth and his wife. Playing it out on a rusting hospital bed, Cumming – stripping himself to the waist, arching his would-be queen seductively over the imagined Macbeth – brilliantly evokes Lady M's sexual power over her husband. Then, lying on his back, his Macbeth submits to the erotic rhetoric contained in both his wife's language and her body.

The piece is stunningly designed by Merle Hensel, whose monolithic hospital room is, it transpires, deceptively versatile; a wheeled chair becomes a royal throne, a bath is a source of elemental metaphor, and the CCTV cameras (and attendant screens) assist the narrative cleverly; not least when Cumming becomes each of the witches in turn.

Co-directed with tremendous ingenuity, and a superb sense of choreography, by recent Tony Award winner John Tiffany and New York theatre maker Andrew Goldberg, this Macbeth (which transfers to New York next month) is, first and foremost, a stunning testament to Alan Cumming's virtuosity.