Tasha's married with two children and still living in her home town near Bristol. While Alice is a high-flying scientist travelling the world with her equally successful husband. But each would trust the other with their life.

So when Tasha and husband Aaron want a break and Alice offers to stay in their home with the kids, Tasha knows they're in safe hands. But she couldn't be more wrong. The call from home is unexpected: Alice and her husband Kyle have been attacked. Alice is in intensive care. Kyle is dead.

Rushing to Alice's bedside, Tasha finds the police trying to piece events together. She can't think why anyone would attack her sister. Then the note arrives, addressed to Tasha: It was supposed to be you .