Jules has been looking forward to her holiday with best friend Kelly and their husbands and children. It's the trip of a lifetime - two weeks exploring the wilds of Canada.
But from the moment they arrive, something feels wrong. There are tensions between Kelly and her husband Damon, a mysterious woman who seems to know them.
When tragedy strikes, forcing them to return home early, Jules is convinced that Kelly isn't telling her the truth about what happened.
Once they are back in the UK, it becomes clear that they are being watched. And Kelly has been keeping more from Jules than she could have possibly imagined.