After making a surprise comeback in Season 6, Sandor Clegane, or The Hound, just got more interesting in the first episode of Season 7 of "Game of Thrones." When Season 6 ended, The Hound was traveling with the Brotherhood Without Banners after Brother Ray, and his friends were killed by rogue members of the Brotherhood.
If you haven't seen the first episode, proceed with caution, spoilers ahead.
The vision in the flames
The Hound and the Brotherhood were traveling north and saw a home. They decided to spend the night there. The Hound was uneasy with the place, it was the home of the farmer who gave him and Arya shelter, and The Hound stole the farmer's silver (in Breaker of Chains, the third episode of Season 4). When the Brotherhood entered the house, The Hound saw the farmer and his daughter's bones in the corner.
The Hound asked Beric Dondarrion why the Lord of Light kept bringing him back to life. Only for Dondarrion to respond that he too doesn't know why. Thoros of Myr started a fire and asked The Hound to look into the flames for answers.
Being the unreligious man that he is, he said that he only saw logs burning. He kept looking, and he described an ominous vision.
"Ice. A Wall of Ice. The Wall. It's where the Wall meets the sea. There's a castle there. There's a mountain. Looks like an arrowhead. The dead are marching past. Thousands of them." Then, Dondarrion asked The Hound "Do you believe me now Clegane? Do you believe we're here for a reason?"
What it could mean
Earlier in the episode at a meeting in Winterfell, Jon Snow asked the Wildlings, headed by Tormund Giantsbane, to guard a castle at the Wall. Jon is raising an army in the North in preparation for the White Walkers coming south.
He wants to build up the defenses in the North and explained that the Wall is the only thing standing between them and the Undead but the Wall has not been manned properly for centuries, with only Castle Black manned.
Jon enlisted the wildlings to man Eastwatch-by-the-sea, the castle closest to Hardhome which was the last place where they saw the White Walkers.
What The Hound saw in flames could refer to what's to happen in the coming battle between the living and the Undead. Eastwatch-by-the-sea could be the castle in the vision, and the Brotherhood is already traveling north. In the Season 7 trailers, we see Jon Snow fighting in the battle alongside Tormund and Dondarrion.
The Hound looks very convinced of what he saw in flames, he even said a prayer when he buried the corpses of the farmer and his daughter. This is an interesting detail from the first episode of Season 7, giving "Game of Thrones" fans much more to look forward to in the coming episodes.