A Feast for Crows
Lambert approaches Queen Cersei Lannister at Lord Tywin Lannister's funeral and promises her the head of her brother, Tyrion. He wears a patch over his good right eye and swears he will not remove it till Tyrion is dead. Ser Jaime Lannister spots Lambert riding at a quintain in the yard of the Red Keep. Lambert is often seen in the court of Queen Margaery according to Taena of Myr.
During his torture, the Blue Bard is forced to list those he claims to have been Queen Margaery Tyrell's secret lovers, including Lambert's name on the list. Cersei has an arrest warrant signed for Lambert as part of her plans to remove Margaery from power. Lambert is sent to the dungeons after his arrest.