On their way to Iolcus, Pelias and his twin brother Neleus, sons of Tyro and Poseidon, meet a strange old woman beside the River Anaurus. Her fell prophecies will stay with the twins and shape their futures.

When they reach Iolcus they meet fellow conspirators in a coup d'état intending to rescue their mother and wreak revenge on the family of Cretheus, their step-father. In the dead of night they attack the palace, browbeating or slaughtering the guards. While one party rescues Perlias' mother Tyro, Pelias himself takes savage vengeance on the woman who took his mother's place, Sidero. Meanwhile a third party attack the royal quarters intent on exterminating the royal family. But with her dying act and the aid of her nurse, the queen saves her newborn son and names him Jason.