Patricia Highsmith (1921-1995) used to come up in (my) conversation most often as an example of a US-born author far more prized in the UK and on the continent of Europe than in the US. The American reading public, usually attracted to authors whose books have been successfully adapted for the big screen, seemed to make an exception for Highsmith, whose first novel, Strangers on a Train (1950), was almost immediately turned into one of Alfred Hitchcock's most memorable films (1951). She went on to publish a total of 22 novels (including The Talented Mr Ripley  and four follow-ups) and seven volumes of short stories, and many of the novels were filmed during her lifetime. US publishers offered rack-sized paperback editions of Highsmith only now and then, whereas she's been a staple of comparable editions in the UK, France and German-speaking countries for 40 years or so. (She lived in Europe from 1963 until her death.)
The success of Anthony Minghella's 1999 film version of The Talented Mr Ripley seemed finally to put Highsmith on the map for US readers--and her arrival in multiple new US ebook editions this year can only help.
A couple of months ago, Highsmith's superb first collection of short fiction, Eleven (1970; also known as The Snail-Watcher and Other Stories) and one of her more accessible stand-alone novels, the twice-filmed Cry of the Owl (1962), appeared in Kindle and EPUB editions.
The Tremor of Forgery (1969), often cited as her best novel--so cited, for example, by Graham Greene, who knew a thing or two about moral ambiguities and 'apprehensive' emotional climates in the world of expatriates. In atmosphere, Tremor will remind some readers of the Camus of The Stranger (also known as The Outsider or L'étranger), others of Paul Bowles (The Sheltering Sky; Bowles was another US-born novelist to whom international readers were more loyal than were readers stateside)--and not just because of Tremor's North African setting. Highsmith's protagonist is Howard Ingham, an American writer who goes to Tunisia to work on a screenplay and, when the film project collapses, stays on to work on a novel. He becomes entangled in (or, it seems at times, liberated by) moral ambiguities. There's a crime or two, and there's seepage in both directions through whatever membrane might separate Ingham's life and work.
For fans of Highsmith (or of Bowles, Greene and Camus), or of 'international' fiction in general, The Tremor of Forgery is a promising choice. But let me mention two other crime classics now available as ebooks, from two grand masters of the Golden Age of crime fiction in Great Britain.
First, Green for Danger (1944) by Christianna Brand (1907-1988). Murder in an operating room during World War II. The quintessential fair-play classic puzzle, and Brand's best-known book. Memorably filmed (1946) with Alastair Sim as Inspector Cockrill.
Second, The Franchise Affair (1948) by Josephine Tey (1896-1952). Half-serious caveat: this is the most nearly Highsmithian novel by the always inventive Tey--and, curiously, the only Tey novel currently available as an ebook in the US. Still, it was named by the Crime Writers' Association in 1990 as one of the 100 best crime novels of all time. A young woman accuses two other women, mother and daughter, of holding her prisoner and mistreating her for a month on their remote country estate. Is she the victim of false imprisonment and abuse, or are they the victims of a false accusation?