Double crossing, finely tuned character studies and an air of homoeroticism: Patricia Highsmith's first novel had all the hallmarks of a Hitchcock thriller so it was small surprise when, in 1951, it became one.

More surprising is the decision to turn Strangers On A Train into a touring stage play as the core audience of Hitchcock fans are sure to know the plot inside out.

Quaintly dated but no less thrilling for that, Highsmith's truly ingenious plot concerns the unexpected dangers of talking to strangers.

On a long-distance train journey, two young men get talking. Guy Haines is an ambitious young architect, Charles Bruno a playboy with a taste for danger.

Guy has a troublesome ex-wife who stands in the way of his marriage to new girlfriend Anne, and Charles a father disapproving of his lavish lifestyle.

As the conversation becomes more drunken, the men cheerfully discuss what it would be like to commit the perfect pair of murders: Guy could kill Charles' father, Charles could kill Guy's ex-wife and, with no evidence to link them to each other, who would ever know?

For Guy it is simply a fantasy, played out to relieve the boredom of a train journey. But Charles has different ideas.

"What's fascinating about playing Guy," says Will Thorp, familiar from Casualty and Strictly Come Dancing, "is that he is essentially the innocent party, yet by the end the audience can hardly relate to him any more.

The play is the story of this nice, normal guy who ends up in a really dark blackmail situation.

"On the other side you've got Bruno, who not only doesn't have a problem with killing but actually seems to find the whole experience quite beautiful. And yet the audience end up feeling sympathy for him."

With EastEnders' Alex Ferns as his stage nemesis, Thorp is also enjoying playing alongside Colin Baker's detective - not least because the two now have Dr Who in common.

"I just appeared in two episodes, The Impossible Planet and The Satan Pit, as a baddie," says Thorp. "I was a human who got the devil in his head and went nuts.

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