The castle tells about one year inside Malpensa international airport, a place where burocracy and security controls put the freedom of passengers, animals and goods through the wringer. The airport is a strategic place where all kinds of Italian police are present. Here, the new security controls are tested: a permanent laboratory where experiments on security are carried out like anywhere else. Secret Italian and foreigner services, Border Police, Treasury Police, private guards, police dogs, cameras everywhere and the constant fear of the next unknown danger. Observing the life inside an airport, we obtain the portrait of a frontier. The film is dramatic, ironic, contemplative and follows emblematic situations through the four seasons.