Cup Harbor was a matriarchal settlement in an abandoned Following Seas Corps facility at the edge of the western ice sheet. The government was a dystopian gynecocracy that believed the only purposes of stallions were sexual pleasure and breeding. Discovering a cure for clone sterility was their primary goal. The population was exclusively unicorn.
The town council had been arranging for the kidnapping and purchase of male unicorns to replenish their stables, as the stallions were treated poorly and had likewise shorter life expectancies. Stallions were often made to fight to establish status rankings and mating privileges.
After discovering the town's practices, Double Down gave the council an ultimatum. If they did not free the imprisoned stallions by the time he returned from Vanhoover, he would kill every adult mare and hang them from the massive tree on the mountainside.
Instead of complying with his ultimatum, the council elders ambushed and captured Double Down on his return trip. Lozenge later freed him, though she hesitated, knowing what he planned to do. This further widened the rift of trust between them.
Over the course of three nights, Double Down systematically killed every adult mare in the settlement. The number of bodies hanging from the tree increased as he took each night's kills back to the tree just before daybreak. He killed the Grand Councilmare last. He picked her off with his sniper rifle as she wept beneath the tree, just as the sun rose on the third morning. He set the fillies and colts free, who would later spread rumors of a vicious, mare-killing stallion named "The Mareslayer".