The actress will be joining other guest stars including All My Children's Cameron Mathison and Rebecca Budig, and television veteran Corbin Bernsen. The episode is set in the world of a fictional daytime soap opera.
Castle centers on a famous mystery novelist, Richard Castle, who is bored with his own success and teams up with the NYPD to help solve the crimes. The series stars Nathan Fillion, Stana Katic, Susan Sullivan, and Ruben Santiago-Hudson.
Seymour debuted on Broadway in the original production of Peter Shaffer's Amadeus, playing Constanze Weber, wife of the title character, and is best known for her portrayal of the iconic title character on TV's Dr. Quinn Medicine Woman. She is currently appearing in Ballroom with a Twist at El Portal Theatre in Los Angeles, partnered with Jonathon Roberts from Dancing With the Stars.
Bernsen is best known for his work on L.A. Law. He has starred on ABC's daytime drama General Hospital and has a recurring role on CBS' daytime drama The Young and the Restless, which stars his mother, Jeanne Cooper.