EXCLUSIVE: The set of the ABC crime drama came to a standstill when lead Nathan Fillion didn’t show up Friday. I’ve learned the actor is in the midst of a contract dispute with producers ABC Studios over his desire for a four-day workweek on Castle, which is in production on its sixth season. It looks like the absence was his way of sending a message. ABC reps say the show continues to shoot this week, and Fillion is on set. The actor plays crime novelist Richard Castle on the show, which debuted in 2009 and sees Fillion partnered with NYPD Detective Kate Beckett (Stana Katic). The series was picked up for another season by ABC on May 13, the same day it wrapped its fifth season. After a couple of tenuous seasons ratings-wise, Castle ranks as the network’s most-watched drama series. Fillion, who hosted the WGA West Awards in February, is repped by ICM Partners.