Silence, Hampstead Theatre, London

Silence may seem a paradoxical title for a show by the excellent Filter, one of whose fortes is using sound to sound the depths of a theme or dramatic situation.

Here, in a piece developed with directed David Farr under the auspices of the RSC, a different kind of silence turns out the to be the uneasy destination of each of the intertwining plot strands. But as with "bugging" movies such as The Conversation and The Lives of Others, the stories involve people who work professionally with sound, which gives a further twist of pathos to the point at when the noise runs out or is withheld.

Played on a stark grey set with state-of-the-art microphones sprouting from silver poles and monitored by an overt sound crew, the production looks as though the proceeding will abstract, but though Filter once again demonstrate their enormous flair for flashing between concepts and cultures and dramatic conceits with a synaptic speed, they are here pressing a stethoscope to the human heart.

Katy Stephens and Oliver Dimsdale both give brilliant, emotionally detailed performances as a thirtysomething married couple whose marriage starts to unravel as they head off on different quests. He is a documentary film-maker who is obsessively intent on getting enough evidence for a film about a secret surveillance unit in the early 1990s that targeted radicals. After receiving an enigmatic unsigned package through the post, she makes a bolt for Russia in search of the Alexei (a deeply moving Ferdy Roberts), the pop entrepreneur she met and loved there in the heady days of the early 1990s. She lost contact with him when he was called up for military service. Once passionate and full of heretical energy, he has dwindled in a self-mistrustful shadow of his former self, now blaming not outside forces, but the enemy within.

Shuttling with extraordinary fluency between past and present and England and Russia and juggling thoughts about the contrasting and converging threats to liberty in autocratic and democratic states, the show handles its material beautifully. There is also a comic subplot in which the film-maker's expert soundman becomes enamoured of the female Australian airline worker who lives in the next-door flat in Hounslow. He bugs her, but fails to speak his love to the lonely woman. Other silences here are more treacherous. A great show by Filter.