Spoiler alert! The following article reveals the ending of "Spiral: From the Book of Saw." Stop reading if you have not seen the movie, now in theaters.
So the British actor, 35, was thrilled to step into the part of wholesome rookie Detective William Schenk, partner to Chris Rock's veteran Detective Zeke Banks, in the horror film "Spiral: From the Book of Saw" (now in theaters).
Finally, Minghella had a chance to put those naturally innocent looks to straightforward use, as young father Schenk earnestly helps Banks hunt down a serial killer who is setting diabolical "Saw" traps for his police victims.
"That was so exciting to me," says Minghella. "William is so wide-eyed, bushy-tailed and clumsy. These are feelings I'm not used to getting to express on screen. I enjoyed that."
Yeah, really great. Until it all turned out to be a big lie. Even the baby sounds were a recording.
We warned you about spoilers. Now's your chance to turn back.
Minghella's character reveals his name is not Schenk after all and he is, indeed, the "Saw" copycat killer seeking long-brewing revenge against a crooked police department that murdered his father before he could testify against cop corruption.
Filmmakers wanted to go against the "Saw" mold cemented by John Kramer, aka Jigsaw (portrayed by formidable actor Tobin Bell), for the franchise reboot. The seemingly non-threatening Minghella was an obvious choice.
"Tobin Bell is a terrifying, amazing actor. It would have been easy to go with that type of character. But we couldn't do that," says director Darren Lynn Bousman, a "Saw" veteran. "I had to go with someone who brought something different. Max is unique. But he also has the ability to turn on a dime."
Minghella says he didn't play his character any differently after the reveal, except for showing Schenk's sociopathic, deranged energy is "playful, like a jester" considering the dark deeds. Shooting the final film moments, Minghella kept to himself on set.
"I didn't want to engage with anybody. I kept myself to myself to preserve a certain kind of energy and attitude," he says. "It wasn't method. But I just wasn't hanging out with anyone."
In the final insidious scenes, Minghella's character sets up the ultimate suspension trap for Samuel L. Jackson's crooked retired police chief Marcus Banks (Rock's onscreen father). His son has the choice of either killing the serial killer or saving his father.
Suffice it to say, neither choice works out as Minghella's mystery killer sneaks off safely before the police open fire, killing Jackson's trapped Banks. The younger Banks is left devastated with glass in his face from a previous "Saw" trap.
"God, I hope people don't throw things at me on the street," Minghella jokes about the reaction after the movie's release.
The actor, whose real-life girlfriend is Elle Fanning (of "Maleficent" and "The Great"), is coy about his inner circle's reaction to his screen inner-evil.
"They have kept this (movie) under lock and key. I just went to a screening last night and my sister came with me," Minghella says. "That's the first time anyone in my life has seen it."
There are questions to be answered if "Spiral" gets the sequel the horror film is clearly telegraphing. Like, should his killer be called Jigsaw 2.0 or simply Spiral?
"You want to call the producers and ask them for me? I'd love to know. I don't know how we're going to approach this," says Minghella.
But if it all works out for a sequel, he's ready to go dark again.
"Chris (Rock) and I talked about it," Minghella says. "The movie, in a very loud way, is asking for a continuation. We're not presuming anything. But we'd certainly be excited to do it again."
This article originally appeared on USA TODAY: 'Spiral' ending: Max Minghella talks 'Saw'-like horrors (spoilers)