Lisa (Stacy Martin) and Simon (Pierre Niney) are young lovers living in Paris, deeply in love but struggling to make ends meet. Simon works in small-time drug dealing to support their lifestyle, but when a client accidentally overdoses during a transaction, Simon flees the country to avoid arrest, abandoning Lisa. Three years later, Lisa has moved on and married Léo Redler (Benoît Magimel), a wealthy, older businessman. While traveling with her husband in Geneva, Lisa unexpectedly crosses paths with Simon. Rekindling their intense passion, Lisa begins a dangerous secret affair with Simon behind her husband's back, setting off a chain of jealousy, guilt, and deadly consequences.