In Barcelona, 1921, it's tense between policemen and anarchists. A military train has been robbed out, and the worth load is stolen. The police then try to find those responsible and get support from the agent Aníbal Uriarte, who was sent from Madrid. The detectives resort to brutal methods and do not even deter from murder. They interrogate the machinist, who could flee, and whom they suspect being connected to the robbery, and then murder him.