Millie is a silver tabby she-cat, a former kittypet. She is first formally introduced in The Sight (first book in the Power of Three series), when she and her mate Graystripe show up on the island that the Clan cats use for Gatherings. Though all the cats in every Clan were glad to see Graystripe alive, they were worried about his kittypet mate. She later has three kits: Bumblestripe, Briarlight and Blossomfall. In Long Shadows, Millie is infected with greencough. Silverstream watches over her, because "Graystripe doesn't deserve to have his heart broken again" due to Graystripe going into a cycle of grief after Silverstream died having his kits. In Sunrise, Honeyfern died saving Briarkit from being bitten by a venomous snake. In The Fourth Apprentice, her kits are seen as apprentices. In Fading Echoes her kits receive their warrior names, Briarlight, Blossomfall, and Bumblestripe.