Then She Was Gone by Lisa Jewell

She was fifteen, her mother's golden girl.
She had her whole life ahead of her.
And then, in the blink of an eye, Ellie was gone.

Ten years on, Laurel has never given up hope of finding Ellie. And then she meets a charming and charismatic stranger who sweeps her off her feet.

But what really takes her breath away is when she meets his nine-year-old daughter.

Because his daughter is the image of Ellie.

Now all those unanswered questions that have haunted Laurel come flooding back.

What really happened to Ellie? And who still has secrets to hide?