Esposito is among subway passengers taken hostage by a mysterious gunman.
Castle and Beckett go under cover as newlyweds at an Old West-style resort to investigate a murder.
An investigation forces Castle into what seems like an alternate world where he and Kate never met.
When crime scene pictures show up on a website, the investigators worry the killer may strike again.
Castle goes under cover to try to find a child who may have information about a shooting.
The investigation into a pool shark's death reveals that the killer may have had paranormal powers.
As the team investigates the murder of a toy company CEO, Castle engages in his own investigation.
Beckett is faced with the toughest case of her career after finding Castle's car engulfed in flames.