A serial killer (Andy Serkis) is terrorizing London.

With the help of a worldwide network of hackers, the Killer is able to spy on random people and catch them doing and saying things online that they wouldn’t want their friends, families, and coworkers to find out about.  The Killer than blackmails his targets, forcing them into committing bigger and bigger crimes for him.  The Killer pushes his victims to their limits and then he arranges for them to die.  Sometimes, he kills them.  Sometimes, he forced them to kill themselves.  The Killer is a smirking sadist, a force of chaos who is empowered by the isolation and loneliness of the modern world.

The Killer’s latest victim is a young cleaner who disappears on a rainy night.  Assigned to the case is DCI John Luther (Idris Elba), a detective who is famous for both his brilliance and his determination.  Luther promises the missing cleaner’s mother (Hattie Morahan, giving a poignant performance in a small but important role) that he will find her son.  The Killer is frustrated to discover that Luther doesn’t spend much time online and, hence, cannot be blackmailed.  However, the Killer’s associates discover that Luther has frequently broken the law in order to catch criminals.  When this information is released to the press, Luther is not only kicked off the force but he also ends up in prison.  All of his fellow prisoners want to kill him.  The police view him as being a disgrace.  Luther has very few allies left in the world but he’s determined to keep the promise that he made to the cleaner’s mother.  When the Killer himself starts to send taunting messages to Luther, Luther decides that his only option is escape from prison and bring the Killer to justice himself.

Luther: The Fallen Sun is a follow-up to the BBC television series, which followed Luther as he worked for London’s Metropolitan Police Service and as he struggled with his own personal demons.  The film begins by bringing Luther’s career as a police detective to a close but it also ends with the suggestion of new career path for John Luther.  In between, we watch as Luther chases the Killer through London and eventually across Europe.  Sometimes opposing  him and sometimes helping him is his former boss, Martin Schenk (Dermot Crowley), and his replacement, DCI Odette Raine (Cynthia Erivo).

Luther: The Fallen Sun is at its best when the action is centered on Luther searching for the Killer in London.  A confrontation between the two in Piccadilly Circus is especially well-done and it leads to genuinely exciting chase through the London Underground.  Idris Elba displays both his fierce intelligence and his exciting physicality, while also doing a good job of suggesting that Luther is always just a frustration or two away from mentally snapping.  Elba is entertaining to watch, a perfect hero for these chaotic times.  Andy Serkis, meanwhile, plays the Killer without a hint of subtlety but that approach works for the character.  The Killer is someone who is evil because he enjoys it.  And, throughout the majority of this film, the Killer really does seem to be having the time of his life.

The film gets off to a good start, with plenty of action and atmosphere.  (This is one of those films where nothing happens unless it’s also raining.)  The aerial shots of London capture a certain neon grandeur that suggests a city that is in the process of transitioning into a brightly lit dystopia.  Serkis’s crimes are genuinely disturbing, with a scene involving a burning building feeling nightmarish in its intensity.  Unfortunately, the film loses its way a bit when the action moves away from England and into Europe.  The more that is revealed about Serkis’s plans, the less sense they make and the more the viewer is forced to suspend their disbelief.  In the end, the film’s third act feels as if it belongs in a totally different movie from everything that came before it.

That said, the mystery is still an intriguing one and Luther: The Fallen Sun actually does have something relevant to say about the illusion of privacy in our extremely online world.  One of the better scenes features hundreds of hackers, all sitting at their cubicles and watching as random people across the world go about their lives.  (“Potential target,” one hacker types.)  Andy Serkis is appropriately creepy and Idris Elba shows off the tough but sensitive screen presence that made him a star.  Luther: The Fallen Sun serves as both an effective continuation of the show and, for the viewers who may be meeting him for the first time, an intriguing introduction to John Luther.