Casting Hugh Bonneville as a psychopathic murderer is just one of the stratagems that elevate “I Came By” above the standard serial-killer thriller, not that it doesn’t adhere to a considerable amount of formula. But having lorded over Downton Abbey since before World War I and been a good friend to Paddington the bear, Mr. Bonneville presents the least likely kind of upper-crust gent to be making young men disappear in chi-chi London. That his character uses a ceramist’s kiln for evidence disposal does, somehow, seem like a concession to branding.
Director Babak Anvari, working from a script he wrote with Namsi Khan, doesn’t attempt to pass off Mr. Bonneville’s Sir Hector Blake—retired jurist and champion of immigrants’ rights—as anything but what he is. There’s no mystery about his place in the story. The dramatic gambit is to make him, initially, more sympathetic than his antagonists. Toby and Jay (George MacKay and Percelle Ascott), young men radicalized by nihilistic YouTubers, have been waging a décor war on the well-to-do of London, breaking, entering, disabling security systems, banishing Alexa and her ilk to the virtual hinterlands and spray-painting “I Came By” on whatever expanse of wall best displays their talents as graffiti artists. The point, as Jay comes to grasp, however slowly, is that Toby is a kind of fundamentalist who’s also mean to his mother. That mom is played by the ever-adorable Kelly Macdonald does not win us over to his anarcho-aesthetic point of view.