The Wallace Shawn season at the Royal Court has been a triumph. Dominic Cooke’s programme is further vindicated by his own revival of a play - starring Jane Horrocks and Lorraine Ashbourne, both superb - that in 1985 sealed a fruitful collaboration between this theatre, and its then director Max Stafford-Clark, and Joe Papp’s Public in New York.

Aunt Dan is the friend of Lemon’s parents who made a deep impression on her when young. Now Lemon, a sickly spinster addicted to fruit and vegetable juices, welcomes us to the theatre as punters in search of a “special treat”. She is obviously related to Shawn’s own alter ego in the new play, Grasses of a Thousand Colours, in the Theatre Upstairs.

Related in the sense of telling us something in a strange, informal manner, as if entranced by her own memory. The play boils down to a discussion of how the unconventional views of Aunt Dan filtered into Lemon’s life, producing in her a philosophical fascination with Nazism – “at least they were trying to create a certain way of life for themselves” – and a profound scepticism about the cult of compassion in modern manners.

What’s great about Shawn is that he can propose these ideas in the voice of a character you may dislike, yet he touches on a nerve in the liberal conscience without sounding loud or stupid; he’s a stylistic master of dramatic casuistry. The central passages of the two-hour play – mostly comprising long monologues – concern Henry Kissinger, the US Defence Secretary during the Vietnam War, and Aunt Dan’s interest in him.

You don’t have to remember Kissinger to get the point about unpopular, even murderous policies, being the price we happily pay for our own well-being, our own cultural security. And when we dive into Aunt Dan’s private life, in a couple of disturbing, sexually explicit sketch implants, we see private colonialism in grisly action to complement the public.

Horrocks is perfect in this role, combining a confidential bedside manner with childish innocence, and she’s technically brilliant, while Ashbourne’s Dan is far fruitier and more sensual than Linda Hunt’s sinister little freak in the original. Good cameos, too, from Paul Chahidi as Lemon’s brutishly Anglophile father, Mary Roscoe as her liberally incoherent mother and Scarlett Johnson as a sexy, vengeful lesbian.

- Michael Coveney