T he sanctity of domestic life shatters in an instant in Gentle Monster , when the home of a French pianist ( Léa Seydoux ) is raided by police. They’re there, she quickly learns, to investigate her husband, the father of her child. Hard drives are seized, on which the police tell her they expect to find large amounts of child sex abuse imagery. What unfolds over the rest of the film is quiet, brutal reckoning: how do you possibly come to terms with the fact that you may have married a monster?

“My agent sent me the script and said, ‘Maybe because you have kids, you might not want to do it,” says Seydoux, sitting reservedly next to the film’s director Marie Kreutzer, in the suite of a London hotel. “I was afraid of the subject, to be honest. But then I read the script, and was actually very moved.…