Castle season 8 Episode 20 promo for coming Monday 8x20 ” Much Ado About Murder ” - After movie star turned theater actor is mysteriously killed, Castle and Beckett go backstage and learn the star had more to worry about than just his lines, on “Castle,” MONDAY. Castle 8x20 Promo “Much Ado About Murder" will be closed captioned in English. Website: http://abc.go.com/shows/castle Air date is May 2nd Monday ABC.