Castle is in Los Angeles with Hayley and Alexis to uncover his missing time when he gets an invitation from the G.D.S. - The Greatest Detective Society. One of their own, Philip Harris was murdered, left in a cemetery and his heart was torn out and left in his hands. The head of the society, Mason Wood tells Castle and he and Kendall Frost are competing for Harris’ open seat on the G.D.S. Whomever solves his murder will get his seat.
Back in New York, Esposito and Ryan investigate the Phantom serial killer whom Harris believed was killing in both New York and L.A. He killed with a knife and always too a piece of each victim. Castle, Hayley, and Kendall Frost end up teaming up to find the killer.
Lanie asks Kevin to do a background check on her new boyfriend and to keep it from Esposito. Ryan tells Espo anyway and he decided to have some fun with Lanie.
Lanie figures out that the knife the serial killer uses has a very distinctive blade.
When Castle thinks a producer, Trevor may be the killer, Hayley and Kendall try to distract him with a threesome date while Castle searches his house but Kendall double crosses him and they all get caught. They find a knife that could be the murder weapon but Trevor says that five of those knives were made for a horror movie.
When Lanie finds that two victims were killed on the same day but on different coasts, Espo and Ryan believe that there are two serial killers.
There are two knives that went missing on the final day of shooting the film.
Castle finds the restaurant where he ate 18 months ago while he was missing. Turns out he had no money and gave the owner his watch but the owner remembers nothing else. Rick doesn’t recognize the watch but buys it back from the owner. Later they find a GPS transmitter inside the watch.
Alexis tracks down who bought the GPS chip in Castle’s watch. She tells Hayley it’s Malcolm McCabe, who is former Army Special Forces. Hayley encourages Alexis to not give the information to Castle as the man is dangerous and no good will come of it. Alexis goes to McCabe’s aunt’s home anyway and sees there is a picture of him with Hayley.
Turns out Hayley was consulting with MI-6 18-months ago when Jackson Hunt asked her to keep an eye on Rick. Rick’s mission in Thailand was over but he had gone rogue and was in L.A. By the time she found him, he had been shot and said he was going to ask his CIA handler, Jenkins to erase his memory. She also says that Castle made her promise not to mention it again.
Hayley claims that she stuck around because she cares about him and Alexis. Then she reveals a video for which only Castle knows the password to watch. On the video he tells himself to forget everything. That he was following the LokSat connection to Bracken but that if Beckett finds out about it, it will get her killed.