WHEN writer-director Juliet Forster needed a framing device for her adaptation of E. Nesbit's The Book Of Dragons, she was struck by two characters from the story of The Deliverers Of Their Country, Harry and Effie.

They duly appear as the dragon detectives who save Britain from a plague of dragons in York Theatre Royal's Studio Christmas show, played by Emilio Iannucci and Elizabeth Mary-Williams in their Theatre Royal debuts.

Both had first auditioned for Forster two and a half years ago for her Studio production of E M Forster's The Machine Stops, another play that called for physical theatre skills now exhibited so delightfully by the duo in the dragon world when playing first-year university student Harry and schoolgirl sister Effie.

In their possession is a book full of tales and legends, handed down from long ago, as well as recent eye witness accounts. "It’s a bit like The X Files for dragons,” says Juliet. “They're the Mulder and Scully of the dragon world."

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Release the dragons: Emilio Iannucci's Harry opens the magical book. Picture: Anthony Robling

Iannucci's Harry and Williams's Effie play the duo at varying ages, bringing the stories they have gathered to life on stage through physical storytelling, animation and shadow puppetry.

"I enjoy performing for children as they're not as polite as adult audiences are!" says Emilio. "When children are watching something, they let you know straightaway if it's interesting or not, which is great, as you have to keep it interesting, keep it fun and have levels of energy to match their levels, if not surpass them."

"There's something magical about performing theatre for children," says Elizabeth. "With plays, children are engaging with something in a way they don't do at school. Live interaction between performers and children in a theatre is a very powerful feeling."

"Some children's theatre talks down to them, which I can't stand, but this play treats them on the same levels as us, and it's great spotting young Harrys and Effies in the audience," says Emilio.

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Elizabeth Mary-Williams as dragon detective Effie in The Book Of Dragons. Picture: Anthony Robling

Elizabeth calls on her aerial circus skills in one spectacular scene. "I trained at Upswing and another company, Scarabeus, training in aerial skills, trapeze skills, ropes and harness work, which is handy for this show," she says.

What about Emilio? "I probably wasn't originally going to be in the air at any point in this show, but because of my love of tree climbing, I am now, but Elizabeth is more skilled. I'm more like 'precise flailing'!" he says.

In childhood, Emilio felt drawn to Smaug, "the really cool dragon" in Tolkien's book The Hobbit, while Elizabeth was "a bit of a tomboy". "So I liked things I wasn't supposed to like, rather like Effie," she says. "I loved space and aliens, Lego and robots, and dragons were definitely up there."

* E. Nesbit’s The Book Of Dragons runs at York Theatre Royal Studio until January 6. The show is advertised as suitable for children aged three upwards and their families, but age five upwards might be better advice. Box office: 01904 623568 or at yorktheatreroyal.co.uk