Glass houses by Francesca Reece

Forester Gethin Thomas is struggling to make ends meet in his rural hometown in North Wales. Bright, charming, but unambitious, the thing that keeps him going is Ty Gwydr, a beautiful lakeside house that he keeps an eye on for absent English owners. The house has been empty for so long he's come to think of it as his own. That is until the owners decide to sell, sending Geth into freefall. And when he discovers that Olwen, his first love who left him and their small town for a new life in London, has returned to North Wales with her husband, Geth and Olwen will find themselves pulled back into the past and what could have been - or still could be. But soon mysterious messages start arriving at the house, and they must question whether this is the love story they thought it was, or whether there might be something altogether more sinister lurking beneath the surface.