ABC announced that Castle had been picked up for a fourth season in January 2011. The initial order was for 22 episodes and then increased to 24 episodes.
Season 4 premiered on September 19, 2011.
Even though Castle and Beckett are both single, both harbor secrets from each other that could destroy their partnership: Beckett that she heard Castle tell her he loved her after she was shot, and Castle that he made a deal that would keep her safe from the conspirators behind her mother's murder as long as she stays away from the case. Through it all, their mutual attraction doesn't dim. Meanwhile, Martha's acting school gets off the ground, Alexis prepares to graduate high school, Ryan plans a wedding, and Lanie and Esposito try to rebuild their friendship after breaking up.