I booked this not knowing anything about it, but just because I tend to book everything the NT has on offer these days, and I skip anything that seems to sink without trace (ahem, Light Shining in Buckinghamshire). I was enthralled from the first, when Denise Gough’s Emma (or is she) made an indelible impression in the waiting room of a rehabilitation facility. From there, Duncan Macmillan’s play manages to make rehab interesting, exciting, and naturally harrowing.

In rehab (for alcohol and pills) Emma, a somewhat unsuccessful actress, meets a doctor and a therapist who resemble her Mum, all played and strongly differentiated by Barbara Marten. Alistair Cope’s Foster is a fellow addict who now works for the facility, and the other inhabitants include Nathaniel Martello-White’s Mark, who is cynical and clever, and Scottish Paul (Kevin McMonagle) who also plays Emma’s Dad.

At first, Emma resists fully. She does not want to be there and sabotages treatment at every possible opportunity. An atheist, she rejects the concept of a higher power and considers herself too bright and well educated to surrender to any irrational concept. At one stage, she recites the plot of Hedda Gabler as her life story, thinking that no one would spot it. The play explains very well the dilemma of many an intelligent addict – how on earth can I get through life, which is essentially meaningless and frequently painful, without a little purchased relief? And why am I unable to stop at a little relief, but must pursue a lot of it?

I find it difficult to articulate precisely why Denise Gough’s performance was so extraordinary. It is a physically demanding role and she throws herself into it. But more than that, she simply takes you inside the mind of an addict with laser-sharp precision. Addicts lie, and Emma lies, right up until the end of the play. We’re never sure whether what she is telling us is the whole truth. She’s a narcissist, like many actors and all addicts, but with the curse of low self esteem thrown in (again like all addicts). Much has been made of the fact that Emma is an actress, but this seems to me to ignore the fact that all addicts are actors. They have to be. They’re all pretending to be someone else, someone who doesn’t need chemical help to get through life. What makes Gough’s performance so utterly amazing are the depths of emotion that are so clearly reflected on her shattered face. It is the finest performance I have seen on stage this year, and I hope that she wins every award going.

The other members of the cast are also very good. Martello-White’s Mark in particular is a realist who knows that he has done awful things in the grip of his addiction. He knows that making amends is a much more difficult thing to do than its benign name suggests. Not all of Emma’s peers in rehab successfully beat their addictions, and the look on Gough’s face when she discovers this will not soon leave my memory.

This is getting a West End transfer and it very much deserves to be seen by a wider audience. It is not a morality tale; it is finer than that. Those who can have one drink and leave it at that should see it, in order to understand the mentality of those who cannot. An absolute triumph.