Almost 10 years after the brutal murder of a British family at a beauty spot in the French Alps, the case remains unsolved. Former investigators and the brother of one of the victims tell the story of the shooting and the ongoing investigation.

Murder victim Saad Al-Hilli's brother Zaid is arrested on suspicion of conspiracy to murder, and leads help investigators uncover a secret marriage, family links to the Iraqi regime, and a Swiss bank account.

Former senior investigating police officer Mark Preston turns the case on its head with a surprising new theory. Investigators admit that mistakes were made, and examine whether the killer could still be found, almost a decade after the shootings.