Documentary exploring the 2012 murder of British computer engineer Saad Al-Hilli, his dentist wife Ikbal, and her mother Suhaila in the woods near Lake Annecy, a case that has gone unsolved for 10 years. Caught up in a media whirlwind, Saad's brother Zaid was eventually arrested under suspicion of conspiracy to murder and accused of organising the killings of his brother and family over an inheritance dispute, but was cleared and released. Telling the full story for the first time, Zaid is joined by former French prosecutor Eric Maillaud, retired British senior investigating officer Mark Preston, and journalist Tom Parry.

The second episode sees Saad Al-Hilli's brother Zaid arrested on suspicion of conspiracy to murder, and follows leads that take investigators to Switzerland, Iraq and the USA. Detectives hunt for a motorcyclist with a distinctive helmet spotted near the crime scene, the FBI help to uncover a secret marriage, journalists dig into connections with the Iraqi regime, and police find a Swiss bank account containing almost a million euros.

The conclusion of the crime documentary asks why so much attention was focused on prime suspect Zaid Al-Hilli, who was eventually released without charge. Former senior investigating police officer Mark Preston turns the case on its head with a surprising new theory, and other investigators examine whether the killer could still be found, almost a decade after the shootings.