When clues in a murder implicate Castle and Beckett's nemesis, Dr. Kelly Nieman, Castle is called in to consult on the case. But as the team delves deeper into the investigation, they uncover connections to notorious serial killer Jerry Tyson.

When an astronaut training for a trip to Mars is mysteriously killed inside a Mars simulation, Castle and Beckett don spacesuits to investigate. But when they discover no one inside the sealed simulation could have committed the murder and no one from the outside could get in, the case takes a shocking turn.