The twelve steps are, of course, those of the Alcoholics Anonymous programme and Keith is a young man recovering from addiction. He has invited an older couple to visit him in his squalid bedsit with its peeling wallpaper and holes in the plaster. We gradually discover who they are and why they are there in what at first appears to be a comedy of ineptitude.
Blake Harrison, making his West End debut, plays Keith, whose jokes sound more like insults. He cleverly keeps the audience unsure whether this is someone none too bright but well intentioned or cleverly contriving. Would he deliberately pass off gravy as a superior coffee or is it an accident? It turns out that schoolteachers Alan and Judith had fostered him and others. Now he seeks their forgiveness for all the trouble he caused them.
Easy-going Alan comes over as a liberal softy who has always found ways to excuse him. Comfortably well-upholstered Barry McCarthy looks exactly right as this man who seems to accept anything rather than have a confrontation. Wendy Nottingham is a wiry contrast as his wife Judy, nervous of the encounter and wanting to cut it short, her unease increasing as things get more problematic.
As the plot moves from the unravelling of the back story to a scary wondering what is coming, its bitter humour turns much darker and, with the arrival of the couple's former head teacher's son (Ben Dilloway), erupts in violence.
Keith has been labelled alcoholic rather than schizoid, but one increasingly feels he's psychotic. As the revelations become more gruesome, Rob Hayes's play certainly has touches of 1960s Theatre of the Absurd and of Grand Guignol (which had its comic strand) but director Tom Attenborough gives this a realist edge, which raises questions about the effect and responsibilities of those in loco parentis, attribution of guilt and the urge to revenge.
You can't explore very deeply in 75 minutes, but as the comic wrappings fall away they reveal something too raw for comfort. That didn't stop a first night audience from applauding it with upbeat whoops as though it had been just light entertainment.