It’s not that I know what to expect from a play by Neil LaBute. I don’t. But I do know that his plays will reach out to my emotions, challenge me and change my thinking in some way. And that is the experience I seek from theatre.

LaBute’s new play The Mercy Seat juxtaposes the horror of the aftermath of terrorism on September 11th with acts of individual cruelty from people of whom you would not expect it. This is what LaBute does really well, he strips away the packaging to expose the darkness at the heart of a relationship, a microcosm of the pit of Western society. In bash a salesman murders his child to get sympathy and promotion as a bereaved parent. The Shape of Things, shortly to appear as a film, is about sexual attraction, looks and exploitation. The Mercy Seat is about greed, opportunity and disloyalty set within two relationships, a man and his marriage and that same man and his mistress.

The Mercy Seat is not really about September 11th but the analysis of a relationship. The devastation of Manhattan is a backdrop to the play and provides the opportunity for Ben (John Hannah) to divest himself of his obligations and responsibilities to his wife and children. The horror of the tragedy serves to expose the ruthlessness of Ben’s self interest. While so many people were being brave here is the ultimate act of cowardice.

The play starts off in a fairly ordinary way until, when you first realise that Ben is pretending to be missing, there is a dramatic shift in the level of interest. The cell phone he chooses not to answer is ringing with calls presumably from his wife and family.

LaBute tightens still further as he analyses the power structure of this relationship between the older woman employer (Sinead Cusack) who on the surface seems to hold all the aces, and her younger employee. This power structure is often expressed as she describes how they make love. He takes her from behind and without being able to look at him she describes what she thinks about. She relates how if he lies to his mistress, as he lies to his wife, his mistress would effectively become his wife. If she is someone he has to deceive, then she is not who he runs to, but whom he is running from.

Finally Abby does the “right thing” and tells him if he wants to be with her, he must divorce his wife and maintain his children, not just disappear. LaBute’s handling of Ben’s reaction to this ultimatum is an unforgiving steel trap even down to the distant way he tells Abby by phoning her from his cell phone while he is in the same room as she is.

The Mercy Seat is an analysis of betrayal more powerful than Harold Pinter’s as it examines not just the man’s motives but the woman’s betrayal of her own sex and the implication of this for the future of their relationship.

John Hannah’s performance has to be weak, cold and cynical, essentially dislikeable and it is. I thought at first that he was in shock such was his limited display of feeling. He is slight and not very tall with boyish good looks. Sinead Cusack as Abby, his boss, twelve years his senior and his lover is a more attractive personality, maybe a reluctant party to Ben’s plan to escape. I can only imagine what Sigourney Weaver might have been like in the role in New York but I would guess that Sinead Cusack might be less the hardened career woman and fractionally more the vulnerable other woman.

Michael Attenborough directs The Mercy Seat with conviction, this his first directorial outing at the Almeida since he took over the artistic directorship. Set in Abby’s warehouse apartment with designer furniture and fine art lining the walls, the environment looks comfortable but we are somehow aware than Ben does not live there. Of course in London we were all voyeurs to the horror of 9/11, transfixed both by the startling visual images and the terrible death toll. The Mercy Seat doesn’t impinge or take away from that experience. Instead it is a small but nonetheless important picture of the depths of inhumanity. Highest recommendation.