As the "Starry Messenger" comet approaches Earth, heralding the culmination of the Witches' dark plan, the Countess Marburg makes a long awaited acquaintance with one who plays a pivotal role in her and the others' cause. Mary and Wainwright grow closer, their mutual affection heightened by recently discovered revelations, but as the pair plans for the next steps along the journey she has in store for him, Sebastian takes matters into his own hands by killing Wainwright out of jealousy. Even as Mary prepares to strike against the Countess, she receives news that shakes her to the core. As Cotton tries to reason out information recently revealed to him, the betrayal of a recently made ally may spell his mortal doom. Meanwhile, Anne continues to glean knowledge from her dead father's writings, and a long-brewing feud reaches a tipping point, culminating in a surprising and potentially game-changing disclosure.