The Unfriend
CHICHESTER FESTIVAL THEATRE

As reflected in the television term “situation comedy”, humour often depends on a fecund set-up. The Unfriend – the debut stage play of Steven Moffat, writer of TV hits including Sherlock and Coupling – starts from a middle- class nightmare.

When English couple Peter and Debbie follow, on a cruise ship, the polite routine of exchanging home addresses with an over- friendly American widow, Elsa, on an adjoining sunbed, she shocks them by break- ing protocol and actually turning up at their west London home. In a further challenge to bourgeois sensibilities, a web search reveals that she may be a serial killer.

This precipitates a sparky farce of manners, in which the couple are too English to ask the pushy visitor to leave, even though she may threaten the lives of them and their children, unnervingly surly teenagers on whom Elsa has a curiously improving effect, leading Debbie to dub her “Murder Poppins”. Some viewers have objected to a lavatorial gag in the second act, involving the possibility that one of the characters has been poisoned, but, learning from Alan Ayckbourn and Michael Frayn, Moffat is maximising the discomfiture of his principal characters; people tempera- mentally incapable of asking their guest if she’s a murderer find themselves forced to launch conversations about a visitor’s bowel movements.