In the Castle episode “G.D.S.,” Castle (Nathan Fillion) goes to Los Angeles to figure out what really happened to him when he was abducted. But he gets roped into a murder case. The Greatest Detective Society (G.D.S.) asks Castle to look into the murder of Philip Harris, a private investigator who was working for a big time Hollywood studio. Castle agrees to investigate but the problem is there’s already a private detective on the case – Kendall Frost.
Detective Kendall Frost is portrayed by Summer Glau. She’s known for her role as River Tam in Joss Whedon’s Firefly (with Nathan Fillion!), The Unit (Crystal Burns), The 4400 (Tess Doerner), Terminator: The Sarah Connor Chronicles (Cameron Phillips), Arrow (Isabel Rochev), and Sequestered (Anna Brandt) among others. Castle airs Mondays at 10pm on CBS.