On 5th September 2012, near a remote village in the French Alps called Chevaline, three members of a British family and a French citizen are found shot dead. As the case attracts worldwide attention, unprecedented human and technical resources are engaged to solve these dreadful murders. Dozens of leads are followed, hundreds of witnesses are interviewed, and endless wiretaps and technical experts are all employed - but to no avail. As every lead turns out to be a dead end, the investigation seems stuck. Then suddenly a new piece of evidence appears. Something that could turn the whole case upside down.