4x13 - Charmed

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.