The 39 Steps at Theatre 3 is a fast-moving comedy thriller

Patrick Galen-Mules, lead actor in the comedy thriller The 39 Steps, says it's as if Steve Martin were cast as James Bond and the whole thing was done in the Monty Python spirit.

Galen-Mules has never seen Patrick Barlow's Olivier Award winner for Best Comedy. Nor has director Jarrad West or the rest of the cast. None of them has read John Buchan's novel and only two have seen all of the 1935 Alfred Hitchcock film that provides the other major source material for Barlow's play.

But that's not necessary: as West says, "I didn't want to colour it. I just want to work from the script."

Not that he was unfamiliar with the Hitchcock style, having seen and loved Psycho and The Birds ("I was terrified by that as a kid") and, most appositely, North by Northwest with its blend of comedy, mystery, romance and thrills: he just wanted to put his personal stamp on The 39 Steps, a play hasn't been done at Rep before.

"What's wonderful about the play is it makes the audience use its imagination ... they have to fill in the pictures themselves."

There are prominent doors in Michael Sparks' set - "it's like a farce" West says - and shadow puppets and plenty of music, although none of the Bernard Herrmann cues familiar from Hitchcock movies will be used, the director says.

"I've got all sorts of fun stuff to put in it - I have to put some Justin Bieber in it: that's my sense of humour."

West says this production is going to reflect "my crazy, wacky sense of humour" and it will provide plenty of opportunities for that. There are only four actors in the cast but three of them play multiple roles, switching characters with the swapping of an accent, a prop, or a costume.

Eighteen-year-old Patrick Galen-Mules is the exception, stucking to one character throughout. He's tackling his first lead role in a play after several recent supporting and ensemble roles in plays and musicals including Malcolm in Rep's Macbeth last year. With a moustache and make-up he's been aged to play the 27-year-old hero, Richard Hannay - originally 37 in the script but made nearly 10 years younger because, the actor says wryly, "I'm a wee baby."

Hannay, he says, is a Canadian visiting London in 1935 who is "pretty fed up with life" and decides to take in a West End show in the hopes of recovering his spirits. He gets more than he bargained for when he meets the mysterious German lady Annabella Schmidt (Steph Roberts) who tells him about a conspiracy before suddenly dropping dead at his home. Hannay, going on the information she has given him, decides to get to the bottom of things and clear his name at the same time and embarks on a dangerous adventure that will be anything but dull.

Although Annabella is dead. Roberts returns twice over the course of the play, first as Margaret, a Scottish crofter's wife and more substantially as Pamela, a young woman who has an initially antagonistic relationship with Hannay and for a time finds herself handcuffed to him, which the actress says presented some choreographic challenges to go with the changes of accent the play required.

"It's hard work but great fun as well."

But if she's busy with three roles, the other two actors playing the versatile "clowns" have an even more hectic time of it. Helen McFarlane plays 14 roles - only one of them a woman - and Nelson Blattman plays 11.

McFarlane - last seen on stage in Rep's The Threepenny Opera - says playing 13 men is "very liberating" and that she's enjoying the challenge of her parts - "lots of character work, lots of voices, lots of different physicality... How I get the character is, I get the physicality and then the voice comes."

Her favourite is the old Scottish crofter Hannay encounters during his travels.

"He's just disgusting ... I love it, I like playing disgusting characters."

She has drawn on memories of The Goon Show and Monty Python for a lot of the various exaggerated British accents she has to employ.

Blattman - in his late teens, like Galen-Mules - was last seen on stage as the phoney policeman Croker in Rep's Wait Until Dark. Here, he plays nearly a dozen characters, everything from an old man to several women, which he calls "a fun exploration".

He says script is written so well it provides plenty to work with and the biggest challenge is that each character has to be given his or her own unique life and physicality, sometimes in a very short space of time, then it's on to the next one as Hannay's adventures continue .