Game of Thrones - Season 6, Episode 5 Synopsis
 

Episode 6 - 5
Title: "The Door"
Directed by Jack Bender
Written by David Benioff & D. B. Weiss
Original Air Date - May 22, 2016

Sansa meets Baelish, who offers the support of the Vale and tells her that Brynden Tully, her great uncle, is gathering an army in Riverrun; she initially refuses his help. Jon and Sansa leave Castle Black to gather support from the other Northern houses, with her sending Brienne to Brynden. In Braavos, Arya is given a second chance to prove her loyalty by killing an actress named Lady Crane. Beyond the Wall, Brandon learns that the White Walkers were created by the Children of the Forest to protect themselves from the First Men. In the Iron Islands, Euron wins the Kingsmoot despite confessing to killing Balon, causing Yara and Theon to flee. In Essos, Daenerys learns about Mormont's greyscale, ordering him to find a cure and return. In Meereen, a red priestess named Kinvara meets Tyrion and Varys and promises to support Daenerys. Brandon's unaccompanied vision causes him to be touched by the Night King, making the cave vulnerable. The Night King, along with White Walkers and hordes of wights, attack the cave, killing the Three-Eyed Raven, several Children, Summer, and Hodor, whose younger self is shown to have been rendered mentally disabled by Brandon's interference.

Source: https://en.wikipedia.org/wiki/Game_of_Thrones_(season_6)