Sam Claflin enlisted the help of a clinical psychologist to get into the mindset of a murderous lieutenant for The Nightingale.
The Peaky Blinders star, 33, plays British Army soldier Lieutenant Hawkins in the period thriller, set in 1825 in a penal colony in Tasmania.
The feature, from The Babadook director Jennifer Kent, follows a young convict, played by Aisling Franciosi, seeking revenge for a terrible act of violence committed against her family.
Claflin and Franciosi filmed numerous scenes of violence together including some depicting rape.
He said: “It took a little while to get into the mindset of a man like that.
“There had to be, unfortunately, a level of understanding as to why a man would make certain choices so I sat down with Jen and a clinical psychologist to discuss why a man would be in that position.
“We drafted, or created, a history, I suppose.
“His history of growing up in a very male-driven family where his mum was probably beaten – he was probably beaten.
“We said he likely had an older brother and he was never quite as good as his old brother, so it was the inferior complex you know.
“And for all those reasons suddenly he’s been gifted an opportunity and he sees gold.
“What was difficult in the actual storytelling of this is I wish there was more vulnerability that you could glimpse.”
Claflin said working with a psychologist gave him a “level of understanding” that informed his work on a “daily basis”.
He added: “But also physically getting into a mindset or a place.
“I think I was very blessed with a very generous cast and crew who would assist me getting to a certain place – whether it’s out of breath or…
“We were constantly being very physical with one another so I felt very well supported.”
Franciosi said it had been important the pair “could really, really trust each other” and could be “extremely vulnerable and fragile” on set.
She added: “We always checked in with each other to make sure that we were both OK, a lot of hugs on set, and I certainly felt very safe with them.”
The Nightingale is released in UK cinemas on Friday November 29.