Shortly after Medea marries King Aegeus, Aegeus’s son Theseus returns from his heroic voyages. However, Aegeus doesn’t know that Theseus is his son. Medea plots to murder Theseus and brews a potion out of foam from the teeth of a mad dog who was dragged from a cave. Medea gives this potion to Aegeus to give to Theseus in a glass, convincing him that Theseus is an enemy. As Theseus goes to drink the potion, Aegeus notices the family crest on his sword. Aegeus knocks the potion away from Theseus’s lips, just barely saving his life.
Medea seems to want to gain power in the world. She betrays her father to marry Jason because she is excited at the prospect of living in Athens. She then commits a series of murders until she finally marries Aegeus—king of Athens. When Theseus returns, Medea likely feels that the king’s son will overshadow her power. In positions of power, men traditionally take precedence over women, so Medea is fighting a losing battle, murdering profusely in her attempt to gain power.
To thank the gods for helping him escape a crime, Aegeus lights fires on altars and hosts a celebration. Everyone gathers to rejoice and tell of Theseus’s heroic exploits. Theseus has killed giants, robbers, and bulls, making the world safer and opening paths to new places. The people call Theseus the most valiant of heroes, and the whole of Athens rejoices.
In contrast to Medea, who uses her magical powers towards evil ends, Theseus is championed in Athens as a hero who has made the world a safer place. Theseus’s return just barely saves Athens from falling under Medea’s evil reign.