The story of the Danaides begins before they were born.
Long ago, there were these two brothers who had some serious sibling rivalry going on. One was named Danaus, and he was the King of Libya. The other was King Aegyptus (a different country - I'll tell you later when I remember). Anyway, each brother was officially friends with the other - but they both wanted the land of the other. What made matters worse was that each brother had FIFTY children. Aegyptus had fifty sons and Danaus had fifty daughters (now what are the odds of that happening, I ask you!). Aegyptus thought this worked out perfectly - his sons would marry Danaus' daughters (the Danaides), and their children would rule both kingdoms.
Danaus was NOT a fan of this plan. Aegyptus' sons were rough and nasty and rowdy and wouldn't have made great sons-in-law. Plus, Danaus was getting a touch of empty nest syndrome - I mean, it's hard to say goodbye to your child, but imagine saying goodbye to FIFTY of them at once! The problem was that King Danaus didn't have the power to begin a war against his brother - Aegyptus had the man power (in more ways than one) to bring a serious conflict to Danaus. So Danaus was afraid that Aegyptus' sons would come and take the Danaides away by force. So "secretly" he built a ship, a BEAUTIFUL ship, with fifty oars, and he fled with his daughters to Greece. They landed in Argos, and the people there saw the ship rowed by the fifty shining princesses and were awed! They made Danaus their king - and since he was trying to AVOID publicity this didn't work out so well. But the people believed that Danaus had been sent from the Gods and wouldn't take no for an answer.
Perhaps he was sent from the Gods, for his reign in Argos was a time of peace and prosperity. That is, until the day that another fifty-oared ship landed in Argos. This may shock you, but SOMEHOW Aegyptus' fifty sons had found out about the Danaides migration and followed to claim their brides. Danaus was still too afraid to oppose them, so he agreed to their demands and prepared a decadent wedding feast - but before they were married he brought his daughters around him. To each of his fifty daughters he gave a dagger and instructed them to murder their new husbands as soon as they were alone.
That may sound like an easy decision: stay with your parents the rest of your life and murder a beautiful and relatively innocent man who loves you, or marry the beautiful and manly man. But it wasn't so simple. Back then, there were laws and things that said people must obey their fathers - especially daughters had to obey their fathers, or risk being turned out without ANY support, which could easily mean death. So when faced with the decision, forty-nine of the Danaides obeyed Danaus and slaughtered their husbands. Only Hypermnestra, the oldest daughter of Danaus, didn't obey. Lynceus, the oldest son of Aegyptus, was damn cool. They talked, hung out, he didn't push her, and they really hit it off. By the end of the night, Hypermnestra was pretty clear that murder was not her goal. The two ran away to avoid Danaus' wrath, and to have a happy life together.
They did, too.
But back in Argos, Danaus and his other daughters weren't having such a great time. Despite his efforts, no one really wanted to marry a princess who had slit her last husbands throat on the marriage bed. I mean, that might turn SOME people on - but no one seemed interested in marriage to that. So basically the rest of the poor Danaides lived the rest of their lives with no companions but each other and VIRGINS! Man. What an icky way to die.
Even Danaus recognized that the whole virginity thing wasn't such a great idea. He needed an heir, and his daughters weren't giving him one. So he had to track down Hypermnestra and Lynceus and bring them back. They ruled Argos after him and had a son named Acrisius. Acrisius had a daughter. And her name was Danae. But that's another story.