Agenor, king of Phoenicia, called his sons together, and it was the day his daughter Europa vanished on the back of a white bull (chapter 42). “Find your sister. Do not come back until you have.”
The brothers took ship and scattered, and Cadmus crossed the sea to wander the land of Greece. Years went by and there was no trace of his sister.
He could not go back and he could not find her. Cadmus went to Delphi and put the question to the oracle, and the answer that came back was strange. “Stop looking.”