Theatre review: Diminished

In one of the better Hampstead Downstairs shows in a while, actor and filmmaker Sam Hoare makes a strong playwrighting debut with Diminished, which director Tom Attenborough sets in a clinical in-the-round space provided by the space's regular designer Polly Sullivan. It's a blank canvas that evokes a mental facility where Mary (Lyndsey Marshall) is being held. Although it takes a while for it to be said out loud it's clear she's there because she killed her severely disabled baby daughter. She'll be pleading diminished responsibility on the basis that depression and exhaustion caused temporary insanity, but with only a couple of days left until her trial she's decided that's not what she wants. She says she knew exactly what she was doing and deserves to serve a full prison sentence, and tries to convince Dr Parker (Rufus Wright) that his initial diagnosis was wrong.

Unsurprisingly Mary's husband Adam (Gwilym Lee) and lawyer Layla (Tamla Kari) aren't happy, and pull out all the stops to avoid her changing her plea.

This is one of those talky plays that had me leaning in to catch everything as, although in theory the arguments here are all around morality and personal responsibility, Marshal's eerily calm performance inevitably raises questions about Mary's mental state that aren't necessarily the ones the characters are discussing - as she herself says, sanity isn't binary, and her subtly manipulative ways seem borderline sociopathic: Almost every scene is between her and one other character because she engineers it so that she's one-on-one with people, and one of the first things we find out about her is that she's read Dr Parker's book so she can quote it back to him and score points.

For a short play this brings up a lot of issues without feeling too overloaded - including, when Mary is visited by the mother (Wendy Nottingham) of a child with the same unnamed disability as her daughter, whether a false plea of insanity would be better for the larger good - it would raise the profile of the condition as part of a tragic rather than scandalous story. I wasn't sure at first about the coda that takes us back to a night when her daughter was still alive and her marriage starting to feel the strain (with a lighting change that reveals something more chaotic hidden within Sullivan's simple set,) but in retrospect we might have been meant to take that as the moment when Mary started to formulate a plan to put her daughter out of her misery: This was the first time Mary met Layla, and perhaps her later unfounded accusations of Adam having an affair with her are actually an attempt to find someone for her husband after she's gone to prison.

It's good to see Gwilym Lee back on stage and looking more handsome than ever - has he done his time on Midsomer Murders now? (I kind of think being a Midsomer Murders sidekick must be a bit like an actor's version of doing National Service. John Hopkins was in tonight's audience, maybe they have a support group.) But this is undoubtedly Marshal's evening, as she makes Mary enigmatic with occasional bursts of emotion. This is certainly one of those plays that offers more questions than answers, but in the good kind of way that leaves you thinking about it and finding new angles on the story for some time after it's finished.

Diminished by Sam Hoare is booking until the 29th of April at Hampstead Theatre Downstairs.

Running time: 1 hour 15 minutes straight through.

Photo credit: Robert Day.