They were discussing this on Woman's Hour today, and it intrigued me. It's being touted as a more realistic Gone Girl-type psychological thriller. I downloaded it this afternoon (less than four quid, not bad) and have just finished. Brilliant, really well-written and convincing.
The rather sad postscript to this first novel's success is that the author died shortly before publication. Do look out for it, and catch the radio 4 piece about it on iplayer if you can.