Spoiler: 3/24/14 episode THE DEATH OF A WALL STREET TRADER PUTS THE TEAM ON A COLLISION COURSE WITH CAPTAIN GATES' SISTER, ON ABC'S "CASTLE" "The Greater Good" – Castle and Beckett investigate the murder of a Wall Street trader, but the case takes a shocking turn when they discover the victim was an undercover informant for the U.S. Attorney's office. To complicate matters further, the U.S. attorney involved is Elizabeth Weston (guest star Salli Richardson-Whitfield, "Eureka"), Captain Gates' estranged sister, on "Castle," MONDAY, MARCH 24 (10:01-11:00 p.m., ET) on the ABC Television Network. "Castle" stars Nathan Fillion as Richard Castle, Stana Katic as NYPD Detective Kate Beckett, Susan Sullivan as Martha Rodgers, Molly Quinn as Alexis Castle, Penny Johnson Jerald as NYPD Captain Victoria Gates, Tamala Jones as Medical Examiner Lanie Parish, Jon Huertas as NYPD Detective Javier Esposito, and Seamus Dever as NYPD Detective Kevin Ryan. Guest Cast: Salli Richardson-Whitfield as U.S. Attorney Elizabeth Weston, Laurie Fortier as U.S. Attorney Stephanie Goldmark, Rosie Garcia as Maria Cordero, Kevin Kilner as Jamie Berman. "The Greater Good" was written by David Grae and directed by Holly Dale.