Sejanus: His Fall, RSC Swan, Stratford-Upon-Avon

Like its main source, the Annals of Tacitus, the play has a connoisseur's interest in the ploys with which the corrupt hold on to power. Doran's production projects, with a black flamboyance, the malign theatricality of Roman tyranny. There are stagey show-trials, in which true patriots, such as Geoffrey Freshwater's furiously righteous Silius, face trumped-up charges of sedition and are driven to suicide. There are public burnings of books that dare to suggest that Julius Caesar's assassins, Brutus and Cassius, are "the last of the Romans", thus insinuating a contrast with the ineffectiveness of the opposition now. Presiding over these travesties of justice is Barry Stanton's deliciously sly Tiberius, a canny political performer to his fingertips in his pose of fey, pious fop.

There's a lovely, droll sequence in which he carefully edges round the trail of blood left on the Senate floor by the dragged-out corpse of Silius. That's the Emperor's philosophy all over: keep clean and at a strategic distance from the monstrous mess you make.

His dirty work is done for him by his favourite, Sejanus, a low-born Praetorian Guard, who, while calculatedly exaggerating the dangers and picking off his enemies one by one, also manoeuvres to become his heir. William Houston delivers a truly scary performance as this fixated overreacher. Power for him is a coldly erotic turn-on: "'Twas only fear first in the world made gods," he declares in a scene where Doran has him working himself up to this rhetorical climax in an act of clandestine, dominant buggery.

Tiberius then enters and asks: "Is yet Sejanus come?" If that may be going an inch too far into joky bad taste, Doran does not need to strain for dark comedy at many other points in the play. Take the brilliant scene in the Senate, when the elated favourite, enthroned and believing that he is to be pronounced heir, is finally toppled. The Emperor doesn't even bother to show up. True to his self-protecting strategies, he effects Sejanus' downfall through a captiously critical letter. The production highlights the neat irony of this by a kind of split-screen effect. Side by side with the effect of this lethal document in Rome, we see Tiberius penning it and reading it aloud in the safety of Capri, petted by the young Caligula.

You can't accuse Sejanus of peddling false hope. Virtuous men - such as Nigel Cooke's tirelessly caustic Arrunitius - are seen to be impotent. The senators' main activity appears to be changing their seating-plan in swift, unedifying response to the latest changes in favour. It's a moment of excessive presumption rather than principled protest that ends the rise of the title character. Nor does his ruin bring closure. The mob demonstrates its fickleness by tearing his corpse to pieces, then instantly regretting its action. The favourite who succeeds him looks likely to be even worse. A pessimistic piece, but not, in the clear-eyed way it shows truth to power, a defeatist one.

In rep to 5 November (0870 609 1110)