One hot August night, Rachel Darcy gets the call everyone fears. It's the police. Her younger sister Evie's had a car crash, she's in a coma. Can Rachel fly to London right away? With Evie injured and comatose, Rachel is left to pick up the pieces of her sister's life. But it's hard fitting them together, especially when she really doesn't like what she sees. Why was Evie driving when she doesn't even own a licence? Who is the man living in her flat and claiming Evie is his girlfriend? How come she has never heard of him? The more mysteries Rachel uncovers the more she starts asking herself how well she ever really knew her sister. And then she begins to wonder if the crash was really the accident everybody says it is. Back in hospital, Evie, trapped inside an unresponsive body, is desperately trying to wake up. Because she's got an urgent message for Rachel - a warning which could just save both their lives . . .