When Wren Irving's numbers come up in the first ever national lottery draw, she doesn't tell her husband, Rob. Instead she quietly packs her bags, kisses her six-month-old daughter Phoebe goodbye, and leaves. Two decades later, Rob has moved on and found happiness with their oldest friend, Laura. Phoebe, now a young woman, has never known any other life. But when Rob receives a mysterious letter, the past comes back to haunt them all. With their cosy world thrown into turmoil, Laura sets out to track Wren down and discover the truth about why she walked out all those years ago.