Det. Slaughter visits Castle’s P.I. office and tries to get his help on a high tech robbery case. At first Castle resists as though he’s scared but then Rick ends up running to help when Slaughter dangles new, cool, story teasers. 

Victor Lee was killed by a giant knife wound. The last person he called was Ethan Slaughter. He was Slaughter’s criminal informant and helping on his burglary case before he was killed. Ryan and Espo get the homicide case and Slaughter says he and Castle will team up with them but then Slaughter holds back information about Lee’s girlfriend. 

CSU finds a print on the hilt of the knife. It belongs to Slaughter. Castle helps Slaughter get away when Espo and Ryan come to arrest him but Castle hides Slaughter from them and the two try to clear his name. 

Victor Lee was mentoring Louis Prince, a 16-year-old genius with a tough background but Victor took advantage of Louis and used his technology to break into the Booth Tower and steal their next generation cell phone chip. But Louis didn’t kill Victor. 

Louis is picked up by a group of armed men trying to find the chip. Slaughter and Castle come to his rescue but are overpowered. Espo and Ryan save them and arrest Slaughter but Castle steals their police car with Slaughter in the back seat. 

Mr. Booth, whose building was broken into by Louis and Victor also had his Cayman islands account hacked and $50 million stolen. Turns out it was Louis’ mentor who once hit on Booth’s wife and got fired from his company for sexual harassment. 

Slaughter agrees to be a mentor to Louis and help get the charges for his crimes reduced. He also admits to Castle that he has an ex-wife who is an opera singer. They met in college when he was a musical theater major. Slaughter tells Castle to stop asking to be let into Beckett’s life and make something happen as well as to put his wife’s needs first.