I quite often say that returning shows have something to prove. Castle really doesn’t: by now you know what you’re going to get, and whether you like it or not. (I still do.) There are new showrunners, it should be said, but both were previously members of the show’s writing team, so I’m not expecting major changes. I wouldn’t be surprised were this to be the final season, mind you; ratings haven’t been great in America, and Stana Katic took a while to sign up this time round, which suggests that costs are getting high, and/or that at least one key member of the cast might be getting restless (tonight, Alibi, 9pm).