True crime dramatisations are generally tedious, but “Des,” directed and part written by Lewis Arnold, is a welcome exception. The three-part series jumps straight in, plunging a London homicide detective (played flawlessly by Daniel Mays) into a serial killing crime scene. A seemingly mild-mannered man has complained about blocked drains, which quickly are found to be jammed with body parts. The man, Dennis Nilsen, AKA Des, quickly confesses, although he never finally reveals if he murdered (and bizarrely treated and regaled post-death) just a dozen men or more. Given that we know the killer within minutes, what is remarkable about Des is the ratcheting tension, aided by a mood of grim horror, but mainly driven by the detectives obsession with finding all the victims’ bodies. And what allows Des to shine is the superlative, controlled, freaky-deaky performance of David Tennant as the serial killer. This is not refreshing viewing but Tennant’s performance lingers after the final frame.