Mel and Harry try to crack the Book of Elders. Macy struggles with her demon side. Maggie competes with Jordan for a promotion. Macy meets a witch named Abigael.

Mel suddenly finds herself haunted by memories of her mysterious breakup with Ruby, while Maggie's demon-hunting habit puts strain on her relationship with Jordan. Harry tries to train the newest Charmed One, but gets derailed when they all must focus on a formidable new nemesis who starts wreaking havoc throughout the magical world.

Mel, Maggie and Kaela, along with Harry and Jordan, have now discovered that the cabal of foes coalescing to bring down the Power of Three are actually working for an ancient evil that's been laying dormant since the dawn of magic. This powerful dark force – known as the Lost One – will be the ultimate test of the strength of the newly discovered sisterhood; forcing them to rekindle their connection...or face the destruction of magic itself.