An ageing fishing boat, Dai-go Fukuryū Maru ("Lucky Dragon No. 5") sets out from the port of Yaizu in Shizuoka Prefecture. It travels around the Pacific, line fishing. While the ship is near Bikini Atoll, the ship's navigator sees a flash. All the crew come up to watch. They realize it is an atomic explosion, but take the time to clear their fishing gear. A short time later, grey ash starts to fall on the ship. By the time the ship returns to port, the sailors have been burned brown. They unload the fish, which are then transported away. They visit the local doctor and then go to Tokyo for an examination. It turns out they are all highly radioactive. Their symptoms become worse, and the contaminated fish causes a panic. The men are taken to hospitals in Tokyo, leaving their families behind. The radio operator, Kuboyama (Jūkichi Uno), dies from the radiation.