When I saw that this book, like Meredith Duran's excellent Duke of Shadows, takes place partially in British India (modern Pakistan), I said "sign me up!" Unfortunately, this is not an excellent book.
Bryony Asquith and Leo Marsden grew up on neighboring estates and then found individual acclaim (him as an explorer and mathematician, her as a doctor and surgeon) before marrying. Though it starts as a love match, things quickly go south. After a year of marriage, they agree to seek an annulment and go their separate ways. Three years later, they meet again in the wilds of Pakistan against the backdrop of a dangerous civil rebellion.
The first third (roughly) of the book serves mostly to drive the reader crazy with unfamiliar place names and, worse, to make both main characters as unpleasant as possible. Bryony is so cold and abrasive, I wondered if she was autistic. It's hard to believe her claims that she loved Leo once, because she seems so aloof and untouchable. Leo is an arrogant golden boy who uses absurdly florid vocabulary and appears to be all charm and no substance.
As the ex-couple make the difficult trek back toward civilization, a series of flashbacks and difficult conversations reveal that the lovers are more sympathetic than they appear and their attraction has not burned itself out, but it wasn't enough to make me root for their reconciliation.
One of the underlying problems in their marriage was sexual dysfunction: Bryony was cold and rejecting whenever Leo pressed his husbandly rights, so he started raping her in her sleep (because by the time she woke up, she was already too far gone to stop him), and he continued doing so even after she begged him to stop, until Bryony killed a patient due to sleep deprivation and finally physically barred her bedroom door to keep Leo out. (Note the lack of spoiler warning, there: I don't believe in hiding rape scenes. In fact, I think books should come with rape warnings the way many erotic books warn of consent issues, anal play, etc. -And, yes: what Leo did was rape, even though Bryony came, and the fact that she turns around and does the same to him (twice!) during their journey does not make it right.) Since they keep up with the sleep-rapes after reuniting, I had a really hard time believing all that was wrong in their original relationship was right in their second-chance romance.
The Pathan rebellion was not nearly as riveting and gut wrenching as the Sepoy Rebellion in Duran's Duke of Shadows, though it was obvious Ms. Thomas borrowed heavily from that book. Duran's story felt so real and horrible I almost felt like I'd been there--I knew what the battle smelled like, and I tasted Emma's terror--but Thomas seems to have concocted the Pathan uprising because she needed some outside drama to get her protagonists out of their own heads and into the sack. Once the lovers' impasse is resolved, so is the military siege. Both resolutions feel a little bit forced and a lot anticlimactic.