Switzerland is deliciously dark and tantalisingly brutal. It’s a psychological thriller that lulls you into a false sense of security, until little by little you realise you’re going to be involved in the most almighty, horrific crash, and there’s nothing you can do about it, but watch.

If you haven’t been to the Ustinov, around the back of the Theatre Royal in Bath, it’s akin to sitting in a tiny seaside picture house. Velvet pull down sofas and a view point so close to the stage you fear any movement might put the actors off their stride. Every cigarette that is lit, you smoke. Every drink that is poured, you can almost smell. You are with the sights, sounds and action in intimate detail throughout the entire play. And what a play it is.

We are taken on a journey into the life of Patricia Highsmith (played by Phyllis Logan), creator of The Talented Mr Ripley. Writer, curmudgeon, recluse. The woman who has created and killed so many characters, is, at the end of her life and coming to terms with her own mortality through a haze of cigarettes and scotch. Enter fresh faced Edward Ridgeway (played by Calum Finlay) who wants her to complete just one more book. Just one more incarnation of Ripley. Just one more murder.

The script is beautifully written. Lyrical and poetic like an unfurling flower, then dirty, racist, antisemitic septic and swear ridden. There are moments of uplifting music and suffocating smoking. The actors both smoke throughout the play, and smoke is even billowing out of the author’s bureau in great plumes. It’s sometimes overkill, but then again, it’s meant to be. We’re meant to be uncomfortable.

Phyllis Logan as Patricia is a complex, irascible delight. She’s both given up on life and still eager to seize the world within her mind. She takes a colossal devil-may-care, overwhelming character and gives her a shivering childlike vulnerability. She keeps us guessing throughout the play. Does she just write about murder, or could she become a murderer? And Calum Finlay. He arrives as Edward wearing an anorak and weighed down with bags like an interrailer. He’s nervous, eager to please. He has the confidence of the young and the double confidence that comes with being American. His character journey is one of a cajoling desperate employee, to a muse inspiring what might be Patricia’s greatest work, to a smooth and cunning adversary. He will get Patricia Highsmith to sign one more book deal. Whatever it takes.

The set is very simple. A book case, table with two chairs, a sofa and a writing desk with seat. To the side, there are windows with pictures of large mountains and to the back of the stage, a window allowing us to see Patricia and Edward retiring to bed. There are few props. Mainly drinks glasses and weapons, which the sour Miss Highsmith collects, but it is simple and sparse. However, in the final scene, when the lights dim and images of New York and tickertapes start to fall, it is a wonderful relief to leave that one room in Switzerland, just for a moment. But someone is leaving for good.

I won’t spoil the end, or amplify the many twists and turns that make Switzerland such a beautifully crafted piece of work, however, I will say that playwright Joanna Murray Smith lulls us into one reality and gives us another. Yes, there are subtle clues, stories and asides that give the characters texture and depth, but like the work of Patricia Highsmith, there’s a shocking, dark ending.

For me, I can’t be neutral about Switzerland, because I have to say I completely loved it.

Switzerland is now showing at the Ustinov Studio at the Theatre Royal Bath until Saturday, September 1. The play is an hour and 40 minutes, with no interval. Please note, there’s a lot of smoking and a fair amount of profanity, so if easily offended this may not be for you. Tickets start at £22.50 and are available by calling the box office on 01225 448844 or visiting www.theatreroyal.org.uk/event/switzerland/