The Promise is a new drama from Terry George (Hotel Rwanda), set amid a horrific genocide in the early 20th century, which Turkey still refuses to acknowledge. The film stars Oscar Isaac as an Armenian caught in Constantinople as the Ottoman Empire collapses.

Charlotte Le Bon, Oscar Isaac and Christian Bale in The PromiseCharlotte Le Bon, Oscar Isaac and Christian Bale in The Promise

"To my shame," Isaac says, "I didn't know about the Armenian genocide before I got the script. To read that 1.5 million Armenians perished at the hand of their own government, it was shocking. To this day, there's an active denial of it. That was the most interesting part of it, but the cast they put together, and the fact that all of the proceeds will go to charity. That's a great thing to be a part of."

The Guatemala-born actor dove into research for the role. "My approach was to immerse myself in the history of the time," he says. "For me, the biggest help was videos and recordings of survivors, who would recount what they witnessed. Little boys, as children, seeing their grandmother bayonetted by the gendarmes, or their mothers and sisters crucified - horrible atrocities! It was heartbreaking. I did feel some responsibility to try and tell their story."

He also felt some unexpected present-day resonance during the shoot, particularly when they were re-enacting a moment when a group of refugees fled into the sea. "The underwater stuff was difficult, especially with a fake beard," he laughs. "Beard number two, beard number three. But then we were watching on the news, and a man jumped in the water to save his wife and kids, but they all drowned. We're seeing the same thing happening over and over again."

Christian Bale and Oscar IsaacChristian Bale and Oscar Isaac

Isaac says there was extra pressure about being on a foreign location. "I do miss home," he says of spending three months in Malta filming The Promise. "It's not like there's an endless well to draw on. Inspiration has to come from somewhere - observing things, reading things, thinking about things. I get a bit nervous if I'm not doing that." To help with this, he always brings his guitar with him (he played in bands before his acting career took off). And he thinks about returning to music if the acting roles dry up.

But for now Isaac will continue mixing smaller projects with higher-profile roles like his hero in the new Star Wars movies or the villain in the last X-Men adventure. "These things go up and down," he smiles. "So there's a sense of, 'Strike while the iron is hot.'"

Watch the trailer for The Promise: