Mike Bartlett is such a talented playwright and with each production he seemingly reinvents his style. Earthquakes in London and 13 were big political plays, Chariots of Fire recreated the film onstage, Cock was about a triangular relationship and his latest King Charles III is about a constitutional crisis and written in iambic pentameters. In conjunction with Paines Plough, comes An Intervention an interpersonal play about two friends, best friends, a man and a woman.

In five scenes, A (Rachael Stirling) and B (John Hollingworth) meet and analyse what their friendship means.  The opening scene is called Harmonica and in it the woman wants to know why the man didn’t come on the march against the government’s decision to send troops to the Middle East, the first intervention of the title.  Her repeated tune is like a few notes on the harmonica, repeated. They have known each other for three years but it’s funny, isn’t it, how we like our friends to agree with us politically, how important this is to us?  They quarrel.

Two things emerge from the first scene which will mar the relationship between A and B and develop as the play goes on.  One is A’s drinking and the other is B’s new girlfriend Hannah.  Their personalities are explored, A’s bubbly, spontaneous personality with her extremes of metaphor, “It’s like playing tennis with a fucking postbox,” on his lack of intervention in their conversation, his lack of contribution, his reticence.  Later scenes see him more involved with Hannah, whom we never meet, as he lives with her and they have a child together.  In the final scene he will choose to intervene in A’s life in a crucial way.

An Intervention looks at the tensions of a platonic friendship between a man and a woman.  There is a beautiful performance from Rachael Stirling as the volatile young woman with an effervescent personality and an intensity, as she self medicates with alcohol.  John Hollingworth’s character is more troubled, introspective, withdrawn, reflective.  It is a parent-child relationship with B’s solid, disapproving parent to A’s irresponsible, free child.  The friendship between them is not expressed sexually, although A is undoubtedly jealous of Hannah, but in terms of conversation and recalling shared experiences.

The final scene has surprises I won’t reveal here for fear of spoiling them, but with a deliciously dark humour.  The very comfortable Watford Palace Theatre space may be a little large for this intense play with its minimalist set.

This is one of Mike Bartlett’s more intimate plays at just 80 minutes without an interval, with a slow but involving burn, as you think about who these characters really are and whether their opposites complement or conflict each other.