When you write a play, you keep your fingers crossed that your leading man won’t suffer a breakdown and scarper to Bruges. Sadly, that’s what happened to Simon Gray during the maiden run of Cell Mates in 1995, with Stephen Fry. The play deserved better — and gets it in Edward Hall’s robust revival. Its success hinges on a compelling performance by Geoffrey Streatfeild as the Cold War traitor George Blake. In Wormwood Scrubs, serving a 42-year sentence for treason, this cagey, babyish, sophisticated simpleton persuades Sean Bourke (Emmet Byrne) to help him escape and abscond with him to Moscow. There, it emerges that the KGB may not let Bourke leave. Can Blake return the favour and help him flee to Dublin? And does he even want to? Three supporting actors do double duty, with chameleonic skill, in English and Russian roles — a device that seems particularly appropriate to this two-faced tale of espionage. Gray’s writing, however, is wholly Anglo-Saxon. He’s more interested in character than in communism. Feelings are repressed, not vented. Yet in the second half, the prolix, evasive, sometimes very funny dialogue achieves a crackling emotional charge.