The ABC show "Castle" stars Nathan Fillion and Stana Katic, with six additional cast members in supporting roles. As of 2015, Seamus Dever, Jon Huertas, Tamala Jones, and Penny Johnson Jerald play workers at the show's 12th precinct. Molly Quinn and Susan Sullivan co-star.
Nathan Fillion stars as Richard Castle, a best-selling author who consults on cases for the New York Police Department. Stana Katic plays Kate Beckett, the homicide detective who serves as Castle's partner and muse. Throughout the course of the show, they solve unusual cases.
Seamus Dever also stars as Kevin Ryan, while Jon Huertas plays Javier Esposito. Ryan and Esposito are detectives and partners who also work with the 12th precinct. Along with Beckett, they strive to solve cases and bring murderers to justice.
Tamala Jones plays Lanie Parish, a medical examiner. She is Beckett's close friend, and her medical expertise proves valuable in many of the cases Beckett and Castle investigate. Penny Johnson Jerald plays Captain Victoria Gates. She replaced Ruben Santiago-Hudson, who played Captain Roy Montgomery until the start of the show's fourth season.
Molly Quinn plays Alexis Castle, who is Castle's teenage daughter from his first marriage. Susan Sullivan plays Martha Rodgers, Castle's mother and a former Broadway actress.