Two friends. One of them went on an anti-war protest, shouted their lungs out, then got staggeringly drunk. The other one stayed at home, watched TV for a bit, and thought about the future.

An Intervention is the new play from award-winning playwright Mike Bartlett and the latest co-production from Watford Palace Theatre and Paine’s Plough, the company behind last spring’s award-winning Jumpers for Goalposts, which went down a storm at the Palace.

If that wasn’t enough of a pull, it also stars the rather wonderful Rachael Stirling, fresh from our screens in the recent hit ITV series The Bletchley Circle, and who has also appeared in Snow White and the Huntsmen and Salmon Fishing in the Yemen, as well as starring in Medea at the Palace in 2012, which was also adapted by Mike Bartlett.

“Mike Bartlett has written something a bit magical,“ says the 36-year-old daughter of Dame Diana Rigg. “It’s brilliant, intense, glorious and incredibly funny. It’s just such a good play.“

Rachael cannot, in fact, stop raving about how good the play is.

“It’s about the trials and tribulations of a friendship,“ says the Kendal Rise resident who stars in the play with John Hollingworth, “and it’s immediately identifiable to anyone who’s ever had a friend.

“My character is a brilliantly bright, funny, slightly bananas girl who probably drinks too much. She’s full of joy and bombastic and full of energy, and her best friend is John’s character – they don’t specifically have names. They’re foils, counterparts to one another, they riff off each other in the way that best friends do, they make one another better somehow, and the combination of the two of them makes for very entertaining viewing.“

The friendship is portrayed in the beginning much in the style of a comedy double act – “a bit like Abbott and Costello, or Morecambe and Wise“ – but as the play progresses, the audience is able to unpick the nature of their relationship.

“I can’t tell you too much,“ Rachael laughs, “but it will become clear when you come and see it.“

Rachael, who is due to start working on a comedy written by Mackenzie Crook when she finishes the play, was asked by Mike Bartlett to be in An Intervention after they worked together on Medea.

“His writing – wow – it just gets me where I want to be got, it’s complicated, brilliant, funny. I’ve never done a two-hander before, but I knew I wanted to do it the minute I read it.

“It has a sting in the tail that none of us saw coming. He’s our best playwright, I think, of our generation, working today.

“It’s very exciting to be a part of.“

  • An Intervention is at Watford Palace Theatre, Clarendon Road, Watford, previews are on April 16, 17 and 19 at 7.45pm, and performances run from April 23 to May 3. Details: 01923 225671, watfordpalacetheatre.co.uk