According to his Twitter bio, it depends on your location but it's the same book.

> His biography of Graham Greene will be released this autumn in the UK as Russian Roulette and in the US as The Unquiet Englishman.

From: https://twitter.com/richardgreene2

Yep, it was retitled for the US market. That, incidentally, happened with a number of Greene's earlier novels (A Gun for Sale, for example, became This Gun for Hire). Later U.S. editions restored the original titles. Interestingly, a request from the publisher to retitle his late novel, The Human Factor, led to Greene changing publishers so while everything before that was published by Viking Penguin, beginning with The Human Factor, his U.S. publisher was Simon & Schuster (and later Reinhardt Books, owned by a friend, for his last novel and the miscellaneous books that gathered many of his uncollected shorter writings).

Cool. Thanks. I probably should have checked that before posting. Russian Roulette is definitely on my shopping list.