When the new season of "Castle" begins, Beckett hasn't heard from Castle since he left for the Hamptons months ago to finish writing his second Nikki Heat novel, "Naked Heat". The most Beckett, Ryan and Esposito have seen of Castle is a bookstore standee of him advertising an upcoming book signing. So when Beckett and her team burst into a shadowy apartment on the trail of a murderer, the last thing they expect to see is the real-life Castle standing over a dead woman's body holding a gun! As Castle protests his innocence, Beckett has no choice but to arrest him on suspicion of murder.

When a coded document hidden by a murdered bail bondsman gets Castle's imagination running wild, Beckett must steer the case back to the violent felons who populated their victim's world - only to discover that maybe Castle's crazy theories aren't so crazy after all. Complicating matters is the surprise arrival of Beckett's ex-partner. As the two reunite over a history that Castle has no part of, Castle is forced to watch the relationship take a turn towards the romantic.