The text message is just three words: I need you. Isa Leigh drops everything, packs up her baby daughter and heads straight to Salten, where she and her three best friends attended prestigious boarding school Salten House. Only Kate still lives in the area, at the crumbling Tide Mill she inherited when her disgraced art tutor father vanished when she was just 17. Each of the women is running from something, from an act that has haunted them for many years but which they have tried their best to bury.

It was supposed to be the perfect holiday, dreamed up by Kate as the ideal way to turn 40: four best friends and their husbands and children in a luxurious villa under the blazing sunshine of Languedoc-Roussillon. But there is trouble in paradise. Kate suspects that her husband is having an affair, and that the other woman is one of her best friends. One of these women is willing to sacrifice years of friendship and destroy her family. But which one? 

Saffyre Maddox was 10 when something terrible happened; she's carried the pain of it around with her ever since. The man who she thought was going to heal her didn't, and now she hides from him, invisible in the shadows, learning his secrets; secrets she could use to blow his safe, cosy world apart. Owen Pick is invisible, too. He's 33 years old and he's never had a girlfriend, he's never even had a friend. Nobody sees him. Nobody cares about him. But when Saffyre Maddox disappears from opposite his house on Valentine's night, suddenly the whole world is looking at him. Accusing him.

When she stumbles across the advert, she's looking for something else completely. But it seems like too good an opportunity to miss: a live-in nanny position, with a staggeringly generous salary. And when Rowan arrives at Heatherbrae House, she is smitten by the luxurious 'smart' home fitted out with all modern conveniences, by the beautiful Scottish Highlands, and by this picture-perfect family. What she doesn't know is that she's stepping into a nightmare - one that will end with a child dead and her in a cell awaiting trial for murder.

Ed finally meets his daughter's boyfriend for the first time. Smart, successful and handsome, Ryan appears to be a real catch. Then Abbie announces their plan to get married. There's just one problem. Ed thinks Ryan is lying to them. All of Ed's instincts tell him his daughter is in terrible danger - but no-one else can see it. With the wedding date approaching fast, Ed sets out to uncover Ryan's secrets, before it's too late....