I am watching you

When Ella Longfield overhears two attractive young men flirting with teenage girls on a train, she thinks nothing of it. The next day, she wakes up to the news that one of the girls - beautiful, green-eyed Anna Ballard - has disappeared. A year later, Anna is still missing. Ella is wracked with guilt over what she failed to do, and she's not the only one who can't forget