Switzerland, the award-winning play about the American novelist Patricia Highsmith by Australian Joanna Murray-Smith, is a remarkable and almost indefinable work, currently being performed by two remarkable actors at Theatre Royal Bath’s Ustinov Theatre. Black comedy, fantasy, thriller, drama, it’s a masterpiece uniting a broad spectrum of genres to brilliant effect.

Whether or not you’re familiar with Highsmith’s most famous work, The Talented Mr Ripley (1954), and her series of novels following the history of manipulative young American serial killer Tom Ripley, Switzerland, first premièred in Sydney in 2014, is a fascinating sub-reality of a writer at the end of her career (and life), who, living as a recluse in the remote Swiss Alps, is visited by Edward Ridgeway (Calum Finlay), a representative of her New York publishing company keen to entice her to sign a new Ripley book deal.

Playing with the often held belief that Highsmith (Phyllis Logan, best known as the matronly housekeeper Mrs Hughes from Downton Abbey) was Ripley, Murray-Smith’s imaginary scenario explores the powerful and almost schizophrenic relationship the author had with her alter-ego; a gripping insight into the mind of one of the most revered 20th century writers. With suspenseful direction by the acclaimed Lucy Bailey that draws us into the writer’s psyche, “Switzerland,” says Bailey, “is a Frankenstein story about a writer who creates her own monster.”

Logan delivers a compelling performance as majestic as the view of the Alps through the living room window (designer William Dudley), with a bitter, droll and sometimes downright menacing portrayal of the racist, foul-mouthed, alcoholic, chain-smoking lesbian writer whose only companions are her cats and snails, yet to be convinced to write another Ripley, the character which has most defined her writing and offered her a release from her own dark and haunting past, “showing the unequivocal triumph of evil over good, and rejoicing in it, too.”

When it’s revealed that Highsmith’s mother, Mary, tried to abort her in the womb by drinking turpentine, later taunting her with the fact, a picture of an anything-but wholesome American childhood emerges. Having no interval adds to the raw intensity, a tone further enhanced by Highsmith’s masculine check shirt and trousers, countless ashtrays filled with half smoked cigarettes and a simple modern set comprising a sofa, table and a writing bureau through which smoke fills the atmosphere to choking point. The audience are meant to feel on edge and they do, while the dialogue is both rich and engaging, with Finlay putting in a slow-burning, layered and sinister performance sure to keep you guessing.

Whilst Highsmith several times tells Ed to take a long walk off a short pier (so to speak), it is his flattery and apparent understanding of her writing style, along with the food items she has requested he bring from America that entices her to keep talking. Although she is less than impressed at receiving the wrong peanut butter and only six cans of Campbell’s Cream of Mushroom soup, the foie gras from Fauchon and a rare collector’s knife, to add to her substantial collection of weaponry, redeems him, as does his willingness to assist her with a plot for the next Ripley novel.

There’s an electric chemistry between Logan and Finlay which intentionally shines a light on both Highsmith’s and Ripley’s ambiguous sexuality, while a Psycho-style tension is ramped up when Highsmith retires upstairs with the knife, perhaps to murder her house guest, doubled when she relates her extensive knowledge of poisons (tasteless and colourless) when serving him eggs for breakfast. Having feared for Ed’s safety, when Highsmith receives a call from none other than the real Edward Ridgeway of New York, we’re not sure who will end up being the victim in this utterly masterful tale of cat and mouse. The only thing inevitable is a West End transfer.

Switzerland at Theatre Royal Bath’s Ustinov Theatre until 1 September 2018. Running time 1 hour 40 minutes with no interval. Production images by Nobby Clark. For more information and tickets please visit the website.