We learned no less a secret than the origin of the White Walkers, but tonight’s episode of Game of Thrones had an even more gut-wrenching revelation in store. When Bran Stark discovers that the benevolent Children of the Forest created the army of ice demons as a doomsday weapon against the human beings who were slaughtering them in turn, it’s a first-hand lesson in blowback. Little does he know he’s capable of a similar moral blood-sacrifice: It’s his own psychic abilities that turned a towering teenager called Willas into the mentally disabled man he knows as Hodor. Mentally time-traveling to the past even as he and his companions flee the Night King and his undead army in the present, the boy burns the defensive command “Hold the door” so deep into his companion’s brain that a truncated version of the phrase becomes all he can say.

The message of tonight’s installment (“The Door”) is that this is the cost of war, even if it’s a battle against pure evil. Half a world away, Daenerys prepares to ride; Tyrion makes alliances with the Lord of Light’s High Priestess; and Euron Greyjoy preps the Ironborn to conquer the world by the Dragon Queen’s side. But even supernatural saviors leave broken bodies in their wake. Hodor’s crippling — along with the loss of the Three-Eyed Raven, the Children, and Hodor himself — shows that the ends may justify the means, but the means are all but unbearable.

I reviewed tonight’s sad, excellent Game of Thrones for Rolling Stone.