How do you get to be the top witch in Salem? It's not by being an especially skilled magic user. It's by manipulating people into doing what you want them to do, and last night's episode all about Mary turning people into her semi-willing pawns—or blaming them for attracting her ire.
It's clear why Mary Sibley is the leader of the Salem witches' coven and not Magistrate Hale. Both Mary and Hale are dealing with the threat of being exposed: Mary at the hands of Mercy and Mr. Hook and Hale at the hands of John Alden. After Anne Hale relates the story of her sickness to Alden, he begins to suggest that Anne's father might, in fact, be a witch, a suspicion that doesn't escape Hale's notice. Since he can't talk Mary into taking Alden out, he takes a "keep your enemies closer" approach with the captain. He invites him to become part of the town's ruling board and tries to come off as an earnest father protecting his father, but Alden isn't buying it. Given how slow Alden is on the uptake, that's a pretty big failure on Hale's part.
Mary Sibley is playing this game at a much higher level, using every Puritan prejudice and anti-Puritan frustration to get what she wants. After Mercy's father expels the snake familiar from her body by performing an exorcism, she shames Cotton Mather for allowing a "pagan" Catholic rite to be performed in Salem and then turns around and convinces Mercy to accept the snake back into her body by reminding her how terrible the Puritans were to her. She recognizes every prejudice and weakness another person possesses and uses it to her advantage.
It's clear that she's still enjoying the power that comes with her position—both as leader of the witches and as George Sibley's wife. When Mr. Hook arrives in town asking her to lift the quarantine on a boat, it seems strange for anyone to question whether she speaks for her husband. In becoming her husband's spokesperson, Mary has become a de facto man in Salem's power structure.
However, she doesn't care what happens to other women in the process. She figures that Anne Hale deserves to be a target on Salem's battleground because she's attracted to John Alden. Mary offers Mercy the power that comes with witchcraft—understanding the desire for that power—but only as a means of trapping her again. And she probably wouldn't have any concern for the prostitute Gloriana, who suffers thanks to Cotton's emotional upheaval. Cotton can't resolve the two parts of himself—the one who wants to be a noble preacher and a worthy son with the one who enjoys a drink and is in love with a prostitute—and when Gloriana arrives in church, trying to goad him into a kiss and an admission of his affection for her, he turns around and rapes her. So much for Cotton being a flawed hero. He's just spiraling, a combination of religious guilt, filial failure, and entitlement fueling him all the way down.
One of the lessons of Salem seems to be that if you feel affection toward another person, you will be manipulated and suffer. Magister Hale must step back from his fight with Mary to protect Anne. Mercy's father risks his life by performing a Catholic exorcism. Anne enters Mary's crosshairs thanks to her attraction to Alden. Cotton's desire for Gloriana conflicts with his need to please his father. Gloriana's affection for Cotton doesn't protect her from rape and humiliation at his hands. And Alden's continued love for Mary makes it easy for Tituba to manipulate him into killing Hook.
On the other hand, it seems like Alden didn't need much of a push to murder Hook. Hook knows something about Alden's past—something that he doesn't want the other residents of Salem to know. Could this dark secret finally make John Alden interesting?
Fortunately, it's also one of the cracks that we're starting to see in Mary Sibley's reign of terror. Mary is putting the entire coven in danger by allowing Alden to continue living, and she doesn't know everything she thinks she knows about her former love. She also doesn't know the real reason that Hook was in Salem, nor who contracted him to deliver the parcel on that quarantined ship. Will Mary's own affection for Alden eventually spark some empathy in her? Or will she finally realize that she's a pawn of Salem's true master of manipulation, the one person who truly seems to have no affectionate feelings for anyone in town: Tituba?