One Of The Best Mystery Shows To Date! 'Castle' follows Richard Castle (Nathan Fillion) as he solves cases with Detective Kate Beckett (Stana Katic), Javier Esposito (Jon Huertas), and Kevin Ryan (Seamus Dever). They go on many adventures, kickin' ass and making quips. With an excellently done mix of mustery, drama, and comedy, Castle stands superior to most mystery shows!