Mindhunter, David Fincher’s thriller based on the true-crime book Mindhunter: Inside the FBI's Elite Serial Crime Unit, returns for a second season on Netflix. The series follows special agents Holden Ford (Jonathan Groff) and Bill Tench (Holt McCallany), who created the FBI’s Behavioral Science Unit in order to interview and profile serial killers with the hope of applying this knowledge to ongoing cases.

Season one saw the two agents sitting down with incarcerated serial killers Ed Kemper (portrayed by Cameron Britton, who earned an Emmy nomination for the role), Montie Rissell, Jerry Brudos and Richard Speck, as they tried to develop a methodology for their evolving research and get inside the twisted minds of these men. 

Jumping ahead to 1979, season two sees the agents taking their work on the road as they continue to interview various notorious killers -- Charles Manson (Damon Herriman) and the Son of Sam, among others -- while also trying to solve two ongoing cases, the Atlanta Child Murders that took place from 1979 to 1981 and the BTK Strangler, who was responsible for killing several people in the Wichita, Kansas, area going back to 1974.   

“The Unit discovered this technique for interviewing killers and understanding their minds,” Groff tells ET about Holden’s journey this season, which sees him getting involved in the efforts to solve the killings of young African-American kids living in Georgia. “Now he's obsessed with taking it on the field and seeing if it actually works in real life.” 

Meanwhile, McCallany says that Bill is being pulled in multiple directions, as he attempts to balance his professional life with his personal one. “He wants to be a good husband and a good father, if he can -- he’s a flawed guy in certain ways but his intentions are honorable -- and he also wants to be a good detective,” the actors says. “His professional integrity is very important to him. And it's the tension that's created from trying to be in two places at one time and trying to divide his attentions and do both sides of his life equal justice that are the source of a lot of conflict in season two.”

For Bill, in particular, that means taking the lead on trying to find out who the BTK Strangler is after the local police force comes up empty-handed. But things hit a little too close to home when it’s discovered a gruesome murder has taken place in his neighborhood, allowing for a bit of paranoia to creep in. 

“Inevitably, they end up taking their work home with them because they become obsessed with trying to find these guys before they can kill again,” McCallany says. “They're constantly thinking about it, constantly going over it and over it and over it in their minds, and studying crime scene photos, and trying to put themselves into the minds of the killers, and they pay a price for that.”

Referring to a quote by Greek playwright Aeschylus, who said, “Wisdom comes alone through suffering,” McCallany says that the same goes for these agents. “We’re all a little wiser by the end of season two, but there was a price to pay along the way.”

Mindhunter season two debuts Friday, Aug. 16 on Netflix.

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