Let’s delve into the episode trailer.
An Empty Throne
First, we see the empty Iron Throne following the death of King Viserys I in episode eight. It’s a mournful and menacing sight as there’s nothing more deadly in the game of thrones than a power vacuum, because of those who seek to fill it…
The Green Council
…enter: Ser Otto Hightower, Queen Alicent and Ser Criston Cole, opening the Small Council session that was set down in Westerosi history books as “The Green Council” (House Hightower’s colours, as opposed to Targaryen black). Otto declares “The King is dead” while (what looks like) Ser Criston cleans the blade of his sword. A grieving Alicent tells the council “He told me he wished for Aegon to be king,” while later in the trailer, Otto issues an instruction that the door remains shut until their business is finished – their business being the fulfillment of Otto’s decades-long wish that his grandson Aegon inherits the Iron Throne.
The Peasants are Revolting
There’s public unrest in King’s Landing as the gold cloaks (knights of the City Watch) push back a crowd of smallfolk running through the streets. By the end of the trailer, we see the crowd gather outside the grand Sept of Baelor – the cathedral that will be destroyed by Cersei Lannister two centuries down the line.
The Lords Bow Down
House of the Dragon’s opening episode ended with the Lords of Westeros pledging fealty to Viserys’ chosen heir Rhaenyra. Here, it looks as though a bunch of them (is that Lord Boremund Baratheon, who originally supported Princess Rhaenys’ claim to the Iron Throne over that of her cousin Viserys?) are kneeling to Ser Otto Hightower, the Hand to the King. (PS. If you’re not bothered about spoilers, pause the trailer at 0:22 for an unmistakable, if out-of-focus, spoiler image.)
Otto’s Secret Agent(s)
This promises to be Otto’s episode, as we see him instruct a mystery long-haired knight with a secret task. “None can know who you are or what you seek.” We later see that same knight (who looks at 0:44 like he has an identical twin) chasing after Prince Aegon, and possibly sword fighting with Prince Aemond ‘One Eye’, though that last one could be a bit of editing misdirection.