One of the best shows to emerge midway through the 2008-2009 TV season,Castlehas a cast and a sense of humor that set it apart from the normal police procedural.  Nathan Fillion plays Rick Castle, a bestselling author of pulpy crime novels who's called in to assist the New York police when a serial killer begins committing copycat murders based on situations in his books.  Castle helps crack the case, then decides to kill off his longtime character and create a new one, named "Nikki Heat," and research her by shadowing Det. Kate Beckett (Stana Katic).  Much to her irritation, he pulls strings with the mayor's office to embed himself in the department, and helps her solve a wide range of whodunits, including a woman drowned in a bath tub full of motor oil, another frozen and suspended at a construction site, and a corpse stuck in a clothes dryer.  To alleviate the grim proceedings, Fillion is in his element as the wisecracking Castle, while adding another ray of sunshine is Castle's impossibly likeable teenage daughter, Alexis (Molly Quinn), who lives with Castle and his mom (Susan Sullivan), a former Broadway star.  Castle's circle of poker buddies includes veteran TV writer-producer Stephen J. Cannell and author James Patterson playing themselves.  Like many (or most) he-and-she cop shows, there's an element of "Will they or won't they…?", but the beautiful Katic keeps Castle at bay by radiating cool.  Clearly she's a woman who wants to separate herself from her emotionally draining and predominantly male job, so it makes it all the more enjoyable when she momentarily steps out of that mode, such as an impromptu appearance at his book signing.  Much to the relief of Fillion fans who feared their man was a show killer after the aborted runs of such shows asFireflyandDrive,Castlewas renewed for a second, full season.--David Horiuchi