After years of investigation, the gendarmes are still facing a mystery. Everything must be started from scratch. A new prosecutor is trying to find the murder weapon, which is quite unique. It is an old Swiss weapon dating back to World War I. Even though it was produced in limited numbers, the search for this weapon is a painstaking task that stretches over months and across multiple countries. Years after the massacre, customs authorities alert the investigation unit: Swiss weapons have been identified, and their owners live near Chevaline. The GIGN is called in for a high-risk arrest—never before have they been so close to their goal.