Perseus, now the rightful heir of Argolis, had to be cleansed of the blood crime of unwittingly killing his grandfather Acrisios, the king. He went to his cousin Megapenthes, son of Proitos  and now king of Tiryns, to be absolved. Still ashamed and reluctant to claim his inheritance, he arranged to exchange kingdoms with Megapenthes, and thus he became lord of Tiryns, and Megapenthes of Argolis

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    Zeus had thought Perseus would be the hero he needed, but now he knew that the hero would come from future generations of that family-the line of Perseus. Time was growing short, though. Already he could hear rumblings beneath the earth as Gaia fashioned the Giants to defeat him.

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    Among the many children of Perseus and Andromeda, the ones important to our story are Alcaeus [Tiryns], Electryon [Mycenae], and Sthenelos [Argos]. Alcaeus had a son Amphitryon and a daughter Anaxo. Electryon married his niece Anaxo and with her had eight sons and a daughter, Alcmena. Sthenlos married Nicippe, daughter of the Hero Pelops. Zeus watched these families closely, and grew more and more confident that the girl Alcmena would be the mother of the Hero. He knew that he himself must father such an important child, but he also wanted him to be born and grow up with every advantage, as a member of a royal family.

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    Zeus was delighted, therefore, when he observed that Alcmena and Amphitryon, heir of Tiryns, had fallen in love. They needed to be married before Zeus could father the Hero, but for this Electryon's approval was needed. That was not easily won. Electryon had married his own niece, and now his daughter wanted to marry her uncle/cousin. Too risky.

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    Then a band of cattle thieves raided Electryon's farm, killed all of his sons, and drove away his cattle. Electryon, broken-hearted, turned to his nephew, Amphitryon.

  "Find these bandits, my boy. Avenge my sons and bring back my cattle. If you succeed, your bride, Alcmena, will be waiting for you."

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    Zeus was now on good terms with himself. It was all working out the way he wanted. Amphitryon assembled his forces and charged after the killers and cattle duffers. However, when he tracked them down he found they weren't a ragtag mob of thieves but a large force of well trained warriors. With his own small band, he had no chance of winning. Instead, he decided to bargain with them.  

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    They were tough negotiators. It cost Amphitryon every ounce of gold he had, but he bought back the cattle and eagerly drove them back to Electryon, knowing he would soon be united with Alcmena. 

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    When the cattle were herded back into his yard, Electryon was delighted. He asked  Amphitryon what he had done with the corpses of the thieves, but Amphitryon had to explain that it hadn't quite worked that way. He explained what had happened, but Electryon was less that impressed. "So you found my sons' murderers, with my cattle which had been stolen. And you didn't punish them? You bought my own cattle back from them?"

   " Yes, that's right. It cost me all the gold I had. I'd be grateful if you would repay me as soon as you can, because now I'm going to support your daughter I'll be needing it."

    " Get out!" snarled Electryon.

     "Can I take Alcmena with me?"

     "You cannot! She won't be marrying you. You've disgraced yourself. You're a coward as well as a fool. Get out!"

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    Amphitryon realised that he'd made total mess of everything, and in frustration threw his club on the ground. The club hit the long horn of a nearby cow, bounced off, and ricocheted into Electryon's head, killing him instantly. Up on Olympus, Zeus held his head in his hands.

    "On this dolt does the fate of the Gods depend?"

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    Alcaeus and Sthenelos, father and uncle of the luckless young man, banished him, but left him with another chance. If he could get himself a proper army and wipe out this formidable gang of cattle thieves, and retrieve the gold he had so foolishly given them, he would be forgiven and allowed to marry Alcmena.

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    First, however, Amphitryon must be cleansed of the blood crime of killing his uncle, [they seemed to commit blood crimes a lot in this family], and so he travelled to Thebes and received the necessary absolution from Creon, the king. While there, he observed that Thebes had a large and powerful army, and he asked Creon if he could borrow it to punish the cattle thieves, who were holed up in Elis, in the Peloponnese.

    If he had the Theban army at his command, Amphitryon knew he could win.