The fourth season of American crime-comedy-drama television series Castle was ordered on January 10, 2011, by ABC. The season aired from September 19, 2011, to May 7, 2012. The fourth season initially contained 22 episodes, but on December 8, 2011, ABC ordered an additional episode, bringing the total episode count to 23 episodes. Penny Johnson Jerald joined the cast as the new captain, Victoria "Iron" Gates for the fourth season. Overview Richard Castle (Fillion) is a famous mystery novelist who has killed off the main character in his popular book series and has writer's block. He is brought in by the NYPD for questioning regarding a copy-cat murder based on one of his novels. He is intrigued by this new window into crime and murder, and uses his connection with the mayor to charm his way into shadowing Detective Kate Beckett (Katic). Castle decides to use Beckett as his muse for Nikki Heat, the main character of his next book series. Beckett, an avid reader of Castle's books, initially disapproves of having Castle shadow her work, but later warms up and recognizes Castle as a useful resource in her team's investigations. Cast Main cast Nathan Fillion as Richard Castle Stana Katic as Dt. Kate Beckett Jon Huertas as Dt. Javier Esposito Seamus Dever as Dt. Kevin Ryan Tamala Jones as Dr. Lanie Parish Molly C. Quinn as Alexis Castle Susan Sullivan as Martha Rodgers Penny Johnson Jerald as Captain Victoria Gates Recurring cast Victor Webster as Josh Davidson Scott Paulin as Jim Beckett Michael Dorn as Dr. Carter Burke Juliana Dever as Jenny Duffy-O'Malley Guest cast Geoff Pierson as Mr. Smith Juliana Dever as Jenny Derek Webster as Mayor Robert Weldon Jennifer Beals as Sophia Conrad Josh Stamberg as Martin Danberg David Chisum as Thomas Gage Lorin McCraley as West Side Wally Meghan Markle as Charlotte Boyd Episodes Reception Critical reception The fourth season of Castle received positive reviews from critics, many of whom was pleased that the show finally united Fillion and Katic's characters Castle and Beckett after having four seasons of on-again-off-again relationship. Sandra Gonzalez from Entertainment Weekly was pleased in the way the relationship happened. DVD release Awards and nominations References 2011 American television seasons 2012 American television seasons Season 4