"Game of Thrones" Season 7, Episode 3 is titled "The Queen's Justice." The episode begins with Jon Snow arriving at Dragonstone to meet with Daenerys Targaryen and plead for her help against the White Walkers. Tyrion Lannister and Missandei are present during the meeting, and Jon and Daenerys have a tense first encounter.
In King's Landing, Cersei Lannister receives the news of her daughter Myrcella's death from Ellaria Sand and the Sand Snakes. She decides to take revenge by capturing Ellaria and Tyene Sand and poisoning Tyene with the same poison that killed Myrcella.
At Winterfell, Littlefinger continues to try to divide Sansa and Jon by suggesting that Jon's loyalty lies with the Starks and not with Daenerys. Meanwhile, Bran Stark returns to Winterfell and shares his visions with Meera Reed, who decides to leave Winterfell.
In Oldtown, Samwell Tarly successfully steals several restricted books from the Citadel and learns about dragonglass, the only substance capable of killing White Walkers.
The episode ends with Daenerys executing one of the two final leaders of the slave cities in Essos, sending a message to the rest of the slave cities and to Cersei that she is not to be trifled with.
In summary, "The Queen's Justice" is the third episode of "Game of Thrones" Season 7. The episode features the meeting between Jon Snow and Daenerys Targaryen, Cersei Lannister taking revenge for her daughter's death, Littlefinger continuing to sow seeds of distrust between Sansa Stark and Jon Snow, Bran Stark returning to Winterfell and sharing his visions with Meera, Samwell Tarly stealing books from the Citadel and learning about dragonglass, and Daenerys executing one of the leaders of the slave cities to send a message to the rest of the slave cities and to Cersei. The episode ends with Daenerys showing her power and strength as a ruler.
