'Criminal Minds' season 12 episode 18 spoilers: Reid starts doubting Shaw; BAU goes underground to catch vampire-like unsub

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Reid (Matthew Gray Gubler) will be showing doubt towards Shaw (Harold Perrineau) who might be his only friend or his biggest threat in prison. Meanwhile, the team tries to catch an unsub that will bring them down into the city sewers.

On the next episode of "Criminal Minds" season 12, titled "Hell's Kitchen," Reid starts doubting Shaw about being the person who would look out for him in prison.

As seen from the episode 18 promo, Reid tells Shaw, "I think you're the one who pulls the strings in here. You have a lot of friends and they play your little game."

However, it is also possible that the stress and hardships of being in prison have gotten to Reid as Shaw, who was surprised by the confrontation, says that the criminal specialist is "losing it."

Meanwhile, Rossi (Joe Mantegna) and his team will be hunting down an unsub who takes his victims at night and hides them from daylight, similar to a vampire.

"The BAU investigates an urban vampire in New York who kidnaps his victims at night and holds them underground in the sewer system. Also, Reid makes an impossible decision in prison that severely affects himself and other inmates," the episode listing on The Futon Critic reads.

While the team works on catching the unsub, it appears that more hard times will happen to Reid until the season 12 finale of "Criminal Minds" comes to pass.

E! Online has confirmed that Shemar Moore will return to the show to reprise his role of Morgan, who will be bringing a significant lead to the BAU that will help the unit in finally catching Mr. Scratch.

However, Moore will only return as a guest — something that disappointed fans of the show who saw his character in the previous season.

"Criminal Minds" season 12 airs every Wednesday night at 9 p.m. EDT on CBS.