ABC is giving Castle a special Sunday test run at 10pm on March 21 with Desperate Housewives as its lead-in (taking Brothers & Sisters slot for the night). Castle will then air in its normal Monday 10pm slot the following night.
This is something some Castle fans have long been suggesting. Castle's ratings have been improving and even a rerun on Monday night performed pretty well; particularly compared to how reruns of some of other ABC's dramas go.
For the first time, Castle will actually have a scripted drama as its lead-in rather than a reality show. Particularly given the show's recent performance ABC's approach of investing (at least a little bit) more while the show is showing strength seems reasonable. Update: Of course, it's actually old news from well before recent ratings strength.
Indeed, Michael Ausiello reported the DH/Castle crossover on January 12- nobody can deny he's good at getting a scoop -- and that one was actually exclusive it was also elusive for me. But if Bill or I had posted it since then, it somehow got lost in all my pre-Lost enthusiasm!