When ABC's Castle last aired in May, Beckett (Stana Katic) lay on the ground, shot. The season four premiere, "Rise," picks up immediately after that moment. Castle (Nathan Fillion) accompanies his partner to the hospital. When she finally wakes up, she claims to not remember anything, and asks Castle to leave her alone for awhile. He reluctantly agrees.
Three months later, Beckett returns to work, having never called Castle. While investigating a new murder, she learns that Castle is working tirelessly to find her shooter, though the new boss, Captain Victoria Gates (Penny Johnson Jerald, 24, Star Trek: Deep Space 9), bans him from the police the station. Having no choice, Beckett must go to Castle to continue to look for her would-be killer, who is still at large. Castle goes over Gates's head to get reinstated, and helps out with both the current case, and Beckett's secret continued investigation into her own shooting.
Gates is certainly a breath of fresh air. While Captain Montgomery (Ruben Santiago-Hudson) finally gets interesting plot right before he is killed off, Gates has a good back story right off the bat. Knowing Gates worked in internal affairs, and is very by the book, Beckett has to sneak around for personal business, something she never does with Montgomery. Also, Castle immediately rubbing Gates the wrong way by going over her head to the mayor means there will be no shortage of friction in the workplace for some time to come. She changes the dynamics of the series completely. Plus, Jerald is a terrific actress, and will certainly bring some dramatic heft in with her.
Castle and Beckett have never been further apart than they are right now. Beckett is lying about not remembering Castle's declaration of love, something she only admits to her therapist (Michael Dorn, Star Trek: The Next Generation, Star Trek: Deep Space 9). Castle lies to Beckett about having a lead on her shooter to protect Beckett's life. With such monumental things kept hidden from the other, they are setting themselves up for a major falling out of trust. Both have their reasons, but that doesn't make their decisions any wiser, if they want to maintain any type of relationship, working or otherwise.