Some unknown maniac is threatening a navigation company to blow up one of its luxury transatlantics, the Britannic, now in high sea with one thousand two hundred passengers. He is asking for a five hundred thousand pound sterling ransom, otherwise the seven bombs aboard will explode. An experienced anti-bomb squad is sent to the Britannic, but although all the bombs are located, a very high skill level will be necessary to dismantle them. Perhaps that task is impossible.