Theseus was recognized when he arrived in Athens by the sword and sandals of his father, Aegeus. The first to recognize them was not Theseus' father, however, but his wife, Medea, originally of Colchis. Medea conspired to make Aegeus poison his son, but Aegeus recognized the sword and sandals in the nick of time and swept the poisoned goblet from his son's hand.
Medea was in Athens because Aegeus had promised Medea safety in exchange for helping him with his problem of childlessness. Medea had been in danger when she made the agreement with Aegeus in Corinth because she was about to commit acts of murder, both through violence and poison.