The following contains spoilers for House of the Dragon Season 1, Episode 4, "King of the Narrow Sea," which aired Sept. 11, on HBO.
House of the Dragon hasn't been short on betrayals, as seen with Otto Hightower pushing Alicent to marry the king to give a royal edge to their family's bloodline. In addition, Daemon partnered with Corlys Velaryon to end the Crabfeeder's threat, which showed the realm that Viserys wasn't a strong ruler.
It's part and parcel of the politics at King's Landing, which is why Viserys has been having so many headaches. And more so, why he wants to ensure Rhaenyra is ready for the turmoil and envy to come. However, the series did hide one bit of backstabbing quite well, and it paid homage to a devious betrayal from Game of Thrones.
The betrayal on House of the Dragon occurred when Daemon got drunk after returning to the capital. He had a brief fling with Rhaenyra, before getting wasted at a brothel. His mistress, Mysaria, woke him up and let him know she was still protecting him. Daemon ridiculed her, though, calling her a "common whore," only to be told she evolved herself and learned of power outside the "skin trade."
As they spoke, a young boy came in and handed money to Mysaria, who then chided Daemon and told him to pay for the room on his way out. The boy, of course, was the same one who informed the Hand of Daemon and Rhaenyra's late-night shenanigans. When the Hand shared that information with Viserys, he made sure not to give up his informant. Audiences, however, had confirmation that Mysaria was his spy, aka the White Worm.
The situation nodded to Varys as the Master of Whisperers from Game of Thrones. But most of all, this threw back to when Shae betrayed Tyrion. He called her a "whore," just to get her away from King's Landing when he went on trial, only to find her in an affair with his dad, Tywin, when he escaped. It resulted in him killing both, although Shae didn't know Tyrion was insulting her to get her as far away as possible, and to safety. Despite being married to Sansa, he loved Shae and hoped someday they could have found a way to be together. Shae, understandably, made her power move, bedding Tywin, lying about Sansa and Tyrion planning against Joffrey, and trying to move up in life as she endured a poverty-ridden, abusive past.
In Mysaria's case, though, there was no endearment from her prince, nor did he ever try to protect her. She knew she was a pawn in Daemon's selfish ambitions, and that he couldn't be trusted. He had a wife, plus he lusted for Rhaenyra in front Mysaria at Dragonstone. To make it worse, he backstabbed her by lying about her being pregnant, all to play games with the king regarding Targaryen heritage.
Breaking tradition could have painted a target on her back should Viserys have wanted to show the Targaryen bloodline wouldn't be sullied. As such, Mysaria picked the side she felt would win: a Hand whose grandson, Aegon, had a claim to the throne. It's a more subtle, secretive betrayal, but one with major ramifications, as Viserys then dismissed Otto as Hand, ordered Rhaenyra to wed Leanor and banished Daemon. In that sense, Mysaria's gamble did backfire, but with Alicent as queen and Otto still manipulating his daughter, Mysaria has a horse in the race. Although, that could change should Daemon find out she turned on him, leading to even bloodier consequences.
House of the Dragon airs Sundays at 9:00 p.m. on HBO and streams on HBO Max.