So for the moment at least, Polly Stenham has found her shtick and is shticking to it.

That Face, the award-winning debut play which in 2007 launched her into the top tier of Royal Court dramatists, and Tusk Tusk, the work that followed it, each featured young middle-class people adrift from the anchor of parental security. So does this third offering, which Stenham, still only 26, has described as the final play of a trilogy.

But although it is a work adorned with witty dialogue, and which eventually builds to a moving climax that evokes the desolation felt by the offspring of absent or dead parents, on this evidence Stenham has not got a great deal more to say on her chosen themes.

This time the vulnerable son and unstable mother — a relationship explored in That Face — is 24-year-old piano prodigy Robin (Tom Sturridge) and sixtysomething widower Lily (Maureen Beattie) who is losing her mind.

Although the drug- and alcohol-consuming son is viewed by his older brother Oliver, an MP, as highly irresponsible, it is Robin who has accepted a terrible responsibility — that of assisting his mother to commit suicide and so escape encroaching dementia.

All the action takes place in a remote family house which designer Tom Scutt evokes by bedecking the Court Upstairs’ space with mounted stag heads and antlers. It is a stuffy setting that has a whiff of old-school thriller about it, minus a suit of armour.

However, Stenham is interested in emotional wounds inflicted by dysfunctional families rather than the kind inflicted by a candlestick in a dining room and, for a while at least, it appears she has found a hugely promising structure by linking the play to each stage of Lily’s suicidal regime of pill-taking.

The countdown is punctuated by a clock’s jokey alarm — the Pink Panther theme — the signal for Robin to administer the next dose of drugs according to instructions set out by Lily when she was of sounder mind.
Through narcotic-induced hallucinations or demented mental lapses, family secrets begin to be revealed.

But with the second act of this shortish play, the plot thins. It sees Robin staving off the moment he has to give up the home he was born in by using all the distractions available to him. These include a working-class scouser drug dealer who he met in a pub, four grams of MDMA which Robin mischievously slips into some cocktails, and Arlo (Joshua James) and Scout (Zoe Boyle), a couple of posh friends who are the Rosencrantz and Guildenstern to Robin’s Hamlet. That is they are actually there not as friends but at the behest of Oliver, who has organised the sale of the house.

Jeremy Herrin’s production is well acted — in the lead role Sturridge has the coiled, vulnerable core of a home-schooled musician who sees no place in a world obsessed with smart phones.

“Everyone’s attached to a screen,” he says. “No one looks at each other any more”, which is true, but hardly an observation we need a playwright to draw our attention to.

When the more worldly Oliver — also very well played by Patrick Kennedy — warns of “the perfect storm” of population growth and resource shortages, the impression is of dramatist searching for something to say about the world and merely coming up with the bleeding obvious.

It is time to find a new shtick, Polly. (www.royalcourttheatre.com)