Castle and Beckett investigate the mysterious death of an Arctic explorer during a polar expedition; Castle soon grows frustrated when realizing that the elusive killer might just be fooling them all.
After a series of suspicious murders occur, Prentiss suspects her old Interpol nemesis, making her fear for the safety of her BAU team as he closes in on her.
Monk must uncover the link between a missing girl and a UFO sighting after Natalie's car breaks down in a small desert town. Daniel Stern guest stars.
Don feels responsible for the death of a participant in the Witness Protection Program after she is gunned down in her home. James Morrison ("24") Guest Stars As Commander Chris Frederickson.
The red cell team tries to find a serial killer who is travelling across the country kidnapping and then hanging his victims.
