The Roman Actor, Swan Theatre, Stratford-upon-Avon

Playing a megalomaniac Roman emperor would, you might have thought, have given Antony Sher the perfect excuse to hurtle headlong in his favourite direction these days: way over the top. But there's a nifty black wit and dynamic variety in his vivid, larger-than-life portrait of Domitian in Philip Massinger's The Roman Actor. The play, a rarely performed tragedy from 1626, is revived now by Sean Holmes in a RSC production full of attractive vigour and incisiveness.

Resembling some peculiarly decadent pit-bull terrier, Sher's shaven-headed tyrant makes psychotic swings between mad-eyed, self-intoxicated belief in his own godhead and feverishly shuddering premonitions of mortality. When fate closes in on him, he's almost winning in the comic way he insists that he's a goner, while also seeking childish reassurance that he'll get a special dispensation from the inevitable. Hurling windy abuse at destiny, he hurriedly backs away like a school bully who is all mouth.

The title is double-edged. It refers both to this despot in the political theatre of the imperial Rome and to Joe Dixon's strapping, gentle giant of a Paris, Domitian's favourite stage performer. History reveals a troubled affinity between actors and tyrants. As types, they are drawn to each other, in part, by kind of professional curiosity, since both survive by putting on a successful public performance. But for the actor, the ironies may be excruciating. How can you satirise the corruptions of the age, if you rely on the patronage and protection of a corrupt absolute ruler?

That's the dilemma at the heart of Massinger's tragedy. But it is one that is eloquently demonstrated by the action rather explicitly spoken about. Indeed, Dixon's likeable, if slightly lightweight Paris is allowed to make a ringing defence of the theatrical profession to the senate, but his argument (that spectators at a play are inspired, by identification, to emulate virtue and to reform vice) is contradicted by the behaviour we see from the court audience at three plays-within-the-play.

The last of these re-enacts the Empress's recent seduction of Paris and Domitian, who has ordered the show, springs on stage and vengefully stabs his protégé in earnest. Excellently directed by Holmes, the resulting sequence is harshly farcical. The dying actor stands aghast, blood spilling from his stomach, while Sher's Emperor, oblivious to his agony, smilingly assures him that it is enormous honour it is to die by the imperial hand and in a dramatic performance. The calm insanity of this episode is beautifully brought out here.

Unlike the band of Stoics, whose bravery under torture is also given an ironically theatrical frame in this production, the actors were prepared, metaphorically speaking, to share a stage with a tyrant. In their leader's case, this willingness has now been taken to a gory reductio ad absurdum.

Not a great play but a very interesting one which Holmes and his cast have done proud.