After a failed assassination attempt by a lone rebel on repressive King Xerses, at the dedication ceremony for the huge guardian statue, rebels approach Dario to get word back to Greece about a secret alliance with Phoenicia, Greece’s enemy, and how Rhodes plans to oppress the people by slavery. Dario is more interested in flirting with the pretty Diala (Lea Massari), daughter of the builder of the Colossus, Carete, but she foils his advances by playfully leading him through a trap door of the underground palace. Not happy on the island, Dario plans to leave for Athens but is told no one is allowed to leave by orders of Thar (Conrado San Martín). He is second in command, and has plans to overthrow King Xerses and with the help of the Phoenicians (they have smuggled in soldiers disguised as Macedonian slaves) made monarch and Diala is to be his queen. When Dario can’t leave, he unwittingly sides with the rebels and tries to leave on their boat. The ship can’t get past the Colossus, and he’s captured but before Dario’s executed as a spy the rebels attack and he’s freed. Returning to see Diala in order to get her to take him to her inventor father, she instead leads him into a trap at the Colossus. He escapes to join the rebels at their camp, but they are slaughtered and those still alive blame him for ratting them out. Dario redeems himself by entering the coliseum, where the remaining rebels are prisoners being sacrificed, and informing the crowd of Thar’s treason. It leads to the thrilling climax, after much political intrigue, and it’s up to Dario to break into the Colossus, open its prison gates and destroy it. When Dario can’t do it by himself, an earthquake saves the day as it scares away Thar’s army and finally destroys the Colossus and the oppressors.