When a pool shark is murdered by an unseen force, Castle and Beckett uncover evidence that the killer may have paranormal powers. Meanwhile, Castle and Beckett attempt to get their lives back to normal following his disappearance.
Beckett and Castle investigate the shooting of an ice cream vendor and clues lead them to suspect that an unknown second grade child might be able to help them solve the case; Castle goes undercover at a school to try and find the student.
When a web celebrity is murdered, Castle and Beckett explore the flashy world of internet fame, but when the killer posts pictures from the crime scene on a photo-sharing site, they realise they are up against a social media sociopath who may strike again.
After Castle finds out that his most beloved 1980's movie star has been murdered, he and Beckett receive aid from a group of older action heroes, and investigate the man's heavily guarded past in hopes that it will lead them to his killer.
Castle is hired to uncover whether a client's husband is having an affair, but the case takes a shocking turn when Castle witnesses the client's murder - by her husband. But with no proof that the killing took place, Castle and Beckett must investigate to expose the truth.
When an astronaut in a Mars simulation is killed, Castle and Beckett don spacesuits and enter the simulation to investigate. Much to their surprise, it seems no one inside and no one outside could have committed the murder.
Beckett and Castle are faced with a large list of possible suspects when a personal injury attorney known as Richie "The Pitbull" Falco is murdered; a shocking secret deepens the mystery surrounding Richie's death.
As Castle and Alexis travel to London, their routine flight turns deadly when the plane's Air Marshal is found murdered. With the help of Beckett on the ground, Castle and Alexis race against time to find the killer before he carries out his fateful plan.