When a prominent astrophysicist is found dead in her car of explosive decompression, Castle is led to theorize her death was the result of an alien abduction, particularly when a government agent (Lyle Lovett) tries to stop the investigation.
- Actor Allusion: Castle can speak Mandarin, thanks to a tv show he used to love.
- Cyanide Pill: Hilariously subverted. Castle stops a Chinese agent from biting down on something by taking the object out of his mouth. Turns out it's just a piece of gum.
- "Eureka!" Moment: Castle has one during dinner with Ashely's parents, realizing that Maria was acting strange and out of character, which a spy wouldn't do, which leads to enough information to catch the real spy.
- The Government: Westfield and his men are searching for the mole who tried to steal vital information from one of their satellites.
- The Mole: Dr. Vaughn worked with the Chinese after receiving a huge gambling debt.
- Vaughn tried to frame the victim as this but Castle and Beckett figured out she wasn't.
- Nice Job Breaking It, Hero: Subverted. Alexis's boyfriend's parents actually like Castle because they find him interesting.
- She Knows Too Much: Maria discovered the satellite Vaughn was selling secrets for and was silenced over it.
- Shout-Out: To the The X-Files. Castle repeatedly whistles the theme and the show occasionally plays it.
- Special Guest: Lyle Lovett guests as The Agent.
- Spy Satellites: Castle, Beckett and the victim thought the object in space was an UFO but it's actually the government's secret spy satellite.
- The Unreveal: The Agent says he has something he needs to tell Beckett in private, but we never learn what it was.
