Petyr Baelish
Not long after Sansa's marriage, Joffrey and Margaery are wed and afterward a grand feast. At Joffrey's wedding, Joffrey is poisoned, and Cersei orders both Tyrion and Sansa arrested. As Joffrey begins to choke to death, Sansa manages to flee during the chaos. Once in her room, she gathers her belongings and notices that one of the amethysts from her hairnet, a gift from Ser Dontos, is missing. Sansa immediately realizes that the prince had been poisoned and starts to doubt Ser Dontos' rescue plan. Understanding that she will be implicated in the murder of Joffrey, she chooses to flee King's Landing with the knight anyway. Ser Dontos is later killed by Petyr Baelish, who reveals that he is the mastermind behind nearly all of the capital intrigue. He reveals that he was the one who sent Dontos to her and that Olenna took the amethyst from Sansa's hairnet.