A young woman is found murdered. Evidence points to Castle by links of jewelry, fingerprints, and emails.
Beckett believes that he is innocent and works to prove it.
While in his holding cell, Castle is visited by Jerry Tyson, the 3XK. He tells him he has been planning this to kill of both of them. Make their lives miserable.
Castle finds an add for a Richard Castle lookalike. They chase the clues back to Tyson who is nowhere to be found.
Castle is cleared of charges and Beckett is sent to bring him back to the precinct for paperwork. While driving back, they are hit from behind by Tyson. He tries to shoot them but Castle shoots him first. He falls off the bridge into the water but his body is not found.
Castle believes that Tyson wanted to be considered dead so he could disappear and get back to killing.
Ryan tells Javi about the Castle/Beckett relationship and Kate tells Lanie herself.