Tom Ridgewood, a mission pilot for a Mars simulation is stabbed to death inside the simulation. All of the other participants have GPS trackers embeded under their skin and no one was near Tom when he was murdered. Due to noxious gases in the simulation to make it more real, Castle, Beckett and Esposito must don spacesuits to enter. Ryan chooses to work from the outside, having no interest in visiting Mars.

Castle and Beckett find an underground facilities tunnel where Clint Granger, the pilot who lost his spot to Tom, tunneled into the simulation. He was secretly getting information from Mikhail, another astronaut in the simulation and selling it to Sir Ian Rasher, a billionaire who was building his own Mars simulation. But neither Clint nor Mikhail killed Tom.

It turns out that the entire team of astronauts hated Tom and didn’t want to spend the rest of their lives on a Mars mission with him. They convinced Mira, their mastermind computer that Tom was a threat to the mission and Mira’s main protocol is to protect the mission. They used Mira to cover up that the Rover was used to stab Tom with a screw driver.

Back at the loft, things have become crowded when Alexis brings over her friends and Martha has her new boyfriend Ben there overnight. Castle decides to call a family meeting. Before he can begin, Martha has an announcement. She’s doing quite well with her work and she suspects that in the near future their will be new little Castles in the loft so she has decided to move out. Castle actually seems a bit saddened that his mother will be moving out but offers to help her in any way he can.