An onstage production of CS Lewis’s “The Screwtape Letters” has become a “scorching” success in Chicago.

The play, based on the book by CS Lewis covers a series of letters written by a fictional devil named Screwtape, giving advice to a younger devil named Wormwood, on how to tempt a man away from God and Christianity.

Max McLean, who produces the show and who originally played Screwtape, said that the popularity of the play was due to its appeal to both Christian secular audiences.

He told the Chicago Tribune, "Lewis is huge with both the Catholic and the evangelical Protestant audience ... For everybody else, the devil always captures the imagination."

According to Michael Cullen, owner of the Mercury Theatre where the show is playing, the Screwtape Letters has become the most financially successful show ever shown at the venue.

Cullen told the Tribune, "It is doing phenomenal business... Every performance has been at or near capacity."

The theatre reporter for the Tribune, Chris Jones, has estimated that the show has been making around $50,000 per week since September from the show, equivalent to almost one million dollars since its run began.

The production was originally meant to run for three weeks in New York in 2006, but proved so successful that it was extended for 11 more weeks and played in Washington DC before coming to Chicago.

CS Lewis, who also wrote “The Chronicles of Narnia”, said that the Screwtape Letters may have been his most difficult book to write.

He said, "I never wrote with less enjoyment ... The strain produced a spiritual cramp."

"The world in which I had to project myself while I spoke through Screwtape was all dust, grit, thirst and itch ... Every trace of beauty, freshness and geniality had to be excluded."

Max Mclean is also the president and executive producer of the Fellowship of Performing Arts, a non-profit organisation that aims to "to produce theatre from a Christian worldview that is engaging to a diverse audience".

Daniel Kelly, a reviewer for NYTheatre.com, said of the production of Screwtape, "Among many of my peers, Christianity is something for bible-thumpers and right-wing conservatives – something that we are predisposed to mock rather than venerate.

“It is therefore doubly important that ironic post-college twentysomethings like myself go and see 'The Screwtape Letters'. What is presented is an intelligent, accessible, bitingly satirical and funny exploration of profound issues of right and wrong. This is not bible-thumping, this is serious meditation on issues having to do with the human experience – and it is important reminder of what Christianity can be."