Basque Country 1968. Txabi Etxabarrieta, a brilliant university student from Bilbao, joins his brother and his group of friends in an unknown organization called ETA. At the same time, Inspector Melitón Manzanas begins to investigate this group of young people.

Two ways of understanding ETA clash in the V Assembly. Txabi takes a step forward with the support of his brother and El Inglés. Melitón Manzanas investigates all his surroundings to gather the maximum information about him.

Txabi and his companions rob a bank. Melitón is pressured by his superiors for not reporting on ETA and its activities, so he intensifies his investigation on the alleged members of the organization that he manages to arrest.

The English press Txabi so that ETA crosses the invisible line and commits its first deadly attack, putting several high Francoist officials in his sights. Melitón believes he has been able to identify Txabi.

Txabi and his colleagues are getting closer to crossing the invisible line, by intensifying their activities and by identifying possible targets. Meanwhile, we know the story of José Antonio Pardines, a Galician civil guard stationed in Guipúzcoa.

ETA's first murder sets off an unpredictable and dangerous chain of events within the organization and in its environment.