Ethan Slaughter (Adam Baldwin) is back and he wants something from Castle (Nathan Fillion) in the upcoming episode of the hit ABC series "Castle."

In "Cool Boys," TV Guide reports that the New York Police Department detective will seek Castle's assistance in a robbery case. Things start to escalate when the heist becomes associated with murder. Now, Slaughter is being tagged as a suspect and Castle does not know whether his friend is guilty or not. Slaughter has been considered a black sheep back in his turf due to his bad reputation. Will Castle agree to team up with him again?

According to Cartermatt, the detective's lack of followers from his department is mainly due to his refusal to follow protocol. It also does not help that when put in an uncompromising situation, Slaughter has the tendency to sell his partner's soul to the devil. His unconventional methods draw no love from those working alongside him, and Castle is aware of this when they toiled in a case before.

Last episode, a rare painting was stolen while on transport. Castle and Beckett (Stana Katic) teamed up to apprehend the culprit whose identity was known by a sole witness to the crime. The victim worked as a courier of precious items and this time, he was carrying a lost van Gogh painting sold for $65 million in a private auction. The witness to the crime, a woman named Mia Lazlo (Stephnie Weir), had a condition called hyperosmia, which means she's the owner of a very sensitive nose.

With very little evidence to work with, they decided to rely on Mia's olfactory prowess. When they eventually found the artwork, "The Nose" told them that it was fake. It turned out the original owner of the painting substituted a forged work for the priceless van Gogh to keep what he believed was his birth right. But Lorenzo (Aubrey Deeker) did not kill anyone, so Castle, Becket, and Mia must search for the killer once again. In the end, they apprehended the victim's brother, who murdered his own flesh and blood for a big payoff.

"Castle" airs Mondays at 10 p.m. EST on ABC.