De Seta uses the wide frame of CinemaScope to capture the ancient ritual of the "mattanza", the killing of an entire shoal of bluefin tuna off the southwest coast of Sicily, a practice that endured for centuries but which has now largely disappeared. The film opens with the rhythms of the waves and the chorus of the "tonnarotti", the tuna fisherman. They wait, sleeping, snacking, and darning nets, with their taut, bronzed skin exposed to the air. When they hear the call signalling that their prey are approaching, having come to warm waters from the Atlantic to spawn, these “peasants of the sea” rise to action. As the men chant together, the tuna are ushered through a series of nets into the "camera delle morte", a central chamber. Working as a group, the men hoist up their nets so that the giant fish can be speared and dragged onto the boat, flapping and bleeding. The water, white from thrashing, turns red. De Seta’s observational eye manifests a keen attention to this traditional process and to the exigencies of collective labour. Like the fish, the men are largely unindividuated, filmed as a mass of bodies united in a common fate. When the slaughter is over, the tonnarotti doff their caps to the dead.