Based on the true story of undercover agent Mikel Lejarza who infiltrated the basque terrorist network ETA in the 70's.
How accurate this film is I cannot say but as far as actionthrillers goes it has surprisingly depth, script and direction above genre standards. The acting is also very good, even down to small supporting roles.
Instead of just delivering easy answers, lame dialogue or bad acting this film asks us questions such as, how the state handles terrorism, how far are you willing to go to reach ones goals, and also about integrity.
This film is without heroes, the main character José María 'Txema' Loigorry / El Lobo (played by Eduardo Noriega) gets forced into this and doesn't really want to be involved.
And his superiors? They are the fascist government lead by no other then dictator Franco who rules Spain with ruthless power.
ETA on the other hand is a terrorist network plagued by inner turmoil, endless discussions about what to do when Franco is gone, and wouldn't be better if ETA put down there guns and became a political party instead? Mix these above themes and add lots of action, sex and you get very well made action thriller pretty far from say, The Bourne Identity (2002).