Castle might be best epitomized in consecutive midseason episodes: in the first, Laura Prepon guest-stars as actress Natalie Rhodes, who has been cast to play the big-screen version of Nikki Heat, and the cast's differing and revolving reactions to her are very funny. The following episode ratchets up the intensity in the newest development in the search for the killer of Beckett's mother. There's also a notable two-parter in which Castle and Beckett are trapped in a freezer as they try to find a dirty bomb somewhere in the city. Other guest stars include Lance Henriksen as an alien-abduction expert, Corbin Bernsen as a soap-opera star, Jane Seymour as a soap writer's mom, Adrian Pasdar as a Homeland Security agent, Bruce Davison as the DA, Michael McKean as a beauty-pageant sponsor, and Gene Simmons as himself. Also appearing are mystery writers Dennis Lehane and Michael Connelly, who leave an empty place at Castle's poker table for the late Stephen J. Cannell. The core of the show, of course, is Castle and Beckett, from the opening of the season when Castle hasn't called or visited the department in months, to Beckett's complicated relationships with her original training officer, Royce (Jason Beghe), or her perpetually absent boyfriend. Then not long after one breathless moment in which it seems "Casckett" might become a reality, things come to a head in the season-ending cliffhanger. --David Horiuchi