Imperium is based on the experiences of FBI agent Michael German, who infiltrated neo-Nazi white-power groups with a view to uncovering terrorist plots of the Timothy McVeigh variety. The movie has Daniel Radcliffe improbably cast as Nate Foster, a nerdy agent whose supposed knack for interpersonal skills – rather perfunctorily established in an interrogation scene – catches the eye of his maverick superior Angela Zamparo (Toni Collette) who recruits him as an undercover operative – diverting him away from what the bureau considers the more pressing jihadi threat. So Nate must shave his head and get the bovver-boots on to pass muster as a white-power extremist and find out about the dirty-bomb outrage Angela suspects they’ve planned. Unlike most movies on this subject, Imperium avoids predictable identity-crisis clichés about the undercover guy coming to like and admire his comrades. But Nate’s miraculous ability to transform himself into a Nazi is never believable. This might have worked better as longform TV; a box set length could give the excellent Collette more to do.