While C. S. Lewis is probably best remembered for his Narnia books, there was much more to him than that. He taught English literature at Oxford and Cambridge, was a close friend of J. R. R. Tolkien and, on regaining his Christian faith as an adult, wrote extensively on that subject. Among the best known of his Christian apologetic books is the satirical novel, The Screwtape Letters, first published in 1942 and still in print today.

In it, Lewis uses the epistolary format of a series of letters from a senior demon, Screwtape, to his nephew Wormwood to address issues of human nature, promoting sin and undermining faith. It has been adapted for radio and comic books and several times for the stage and now Sydney theatre company Clock & Spiel Productions is bringing its own stage adaptation of the book – approved by the Lewis estate – to Canberra.

The show is a dark comedy that follows the correspondence between Screwtape – played by Yannick Lawry – in some underworld and Wormwood, who never appears.

"All the correspondence is one way," Lawry says.

Wormwood is counselling his nephew whose task it is to secure the damnation of a young man, known as "The Patient," in the best ways to go about, as Lawry says, "edging him away from the light [and] towards the nothing".

To avoid monotony and an inappropriate feeling that the piece is like a sermon, Hailey McQueen's adaptation also includes the book's servant character Toadpipe, played by George Zhao, whose experience ranges from opera to Commedia dell'Arte.

"It's definitely not static," Lawry says.

"He waits on Screwtape hand and foot and explains some of the knottier details of the text – and he provides comic relief in what is intended as a thought-provoking, accessible examination of issues of religious faith and human nature."

In talking about the point of The Screwtape Letters, Lawry cites an apposite quotation from the American theologian A. W, Tozer: "The devil is a better theologian than any of us and a devil still." Screwtape, he says, has of necessity a shrewd understanding both of the Enemy – that is, God – and of human nature in the battle for the soul of "The Patient", a representative of souls of all humans.

For the play, McQueen removed many of the references to World War II, which was going on when it was published. Other seemingly dated references have acquired new meaning: at one point reference is made to writing a "post" about something, which in the 1940s might have referred to a telegram, Lawry says, but now can be taken to refer to the digital age, even though that wasn't the original intention – pointing to the underlying timelessness of the text.

While The Screwtape Letters will obviously be of particular interest to Christians and Lewis fans, Lawry says audience members have come up to him after performances and said that even though they aren't believers, the play has given them a lot of food for thought.

He says he and McQueen met a few years ago while working on a play and she told him about her ambition to adapt The Screwtape Letters for the stage. Although, as a Christian himself, he had heard of it, he had never read it until then. He was "captivated" by the book, which he found was still extremely relevant and even, in some ways, confronting, raising questions about how much power people have over their lives and decisions. But evil isn't an entirely external force to blame for everything that goes wrong, Lawry says: humans may not be able to control what tempts them or when or how, but they can control how they deal with it.

It took a few drafts before the Lewis estate and the creators were happy with the adaptation but it was finally produced last year – first, in a pilot production financed partly through an alumni loan from McQueen's old college, now as fledgling theatre company Clock & Spiel's first production. After a return season in Sydney this year, The Screwtape Letters is going on tour, beginning with Melbourne then Canberra.

Lawry, 39, was born in Britain and graduated from Arts Educational Schools, London, with a masters in acting in 2003. He has worked on stage, in television, film and radio. He came to Sydney in 2008 intending to stay for six months but ended up liking it so much he stayed on and became an Australian citizen this year.

"I like the lifestyle in Sydney – I'm quite outdoorsy, I like camping, the outdoors, sport," Lawry says.

He has found work in radio and acting here and is also studying for a certificate in theology at Moore College.