Based on the true story of an undercover agent responsible for the arrest of dozens of terrorists after he penetrated the upper ranks of the Basque terrorist group known as ETA. Down-on-his-luck Txema is friends with several members of ETA. When cop Pantxo approaches Txema about infiltrating the group, Txema is uncertain until secret service agent Ricardo writes him a check and turns him into The Wolf. At a wedding, Txema falls for Amaia, who tells Txema the kind of insider information Ricardo wants to hear. Tension mounts as Txema and Amaia carry arms across the French border, get involved in a kidnapping and start planting bombs. As the stakes rise, Txema offers his services to hardliner Nelson, who is now Ricardo's target. Amaia is seduced by Nelson's charisma and Txema now realizes his new life has brought him more than he bargained for.