The Beast Must Die is not precisely an easy novel to translate from page to screen, especially after nearly 100 years. The book, which is authored by Nicholas Blake, the pen name of Cecil Day-Lewis, is a book very much of its pre-World War II era, about the male condition, men vs. men, and white men at that. It centers around a crime writer, Frank Cairns (who also happens to write under a pen name), and the death of his son in a hit and run and his planned revenge, figuring that his crime writing occupation has given him the ability to pull off the perfect crime.
With such a pedigree, one would expect an adaptation, even one that is choosing to make as many changes to the story details as this, to focus on Cairns. Now renamed Frances (Cush Jumbo), she is the mother of the deceased child, who will eventually land on the quarry on which she's focused: George Rattery (Jared Harris).
And in the show's first shots, the series plays like that's the plan, with Jumbo's eyes looking directly into the camera, declaring she's here to kill a man as images from the hit and run of her son, Marty, flash before our eyes. But then the show takes a 180 degree turn to DI Nigel Strangeways (Billy Howle), a PTSD suffering detective who has turned his entire life upside down in desperation to get a handle on his mental state. He's left London; he's moved to the Isle of Wight, where he's taken over the lead position after the recent passing of the station's long-time detective.
Due to the funeral of this man he never met, Strangeways is the only one in the office, along with PC Asha James (Aasiya Shah), when Cairns arrives in a cold rage because his now-dead predecessor has closed the case without solving who killed her child. He puts her off, covering for the station and the man who worked here before him, even as it becomes clear nothing was actually done about this case
He's also talking to his therapist, Dr. Blout (Nathaniel Parker), in a scene that soon becomes clear is one after the fact. He's the narrator of this story and (despite the show's pedigree suggesting otherwise) the central figure. It might seem like an odd choice for a standalone series. But as fans already know, this isn't a one-and-done. BritBox, which commissioned the series, is already doing a second one starring Strangeways to turn him and his determined to do the right thing detective into a running series. And the setup works well. After all, in a town this small, it's not really policing; it's social work, with Strangeway's underlings, like Vincent O'Brien (Douggie McMeekin) busting teens for peddling fake IDs.
No wonder Strangeways' incompetent predecessor couldn't handle the only case of interest when it landed on his island. Nor should it be a surprise that it's the only one Strangeways cares about, and that given a chance to see where the hit and run happened, he makes O'Brien stop the car. Cairns' case has become the only thing that distracts him from the ongoing PTSD, tied to the death of his colleague, who we learn was shot in the face during an incident on the job.
Meanwhile, despite centering Strangeways, the show does follow Cairns as well. Upon returning to London, she gives up her job as a teacher, cashes out her saving, changes her name, and declares she's becoming a crime writer. Haircuts and a new home follow to a nice cottage on (where else) the Isle of Wight. While Strangeways pokes about at the case on one side of the Isle, on the other, she starts watching the traffic and asking questions of the neighbors, the garages, tracking every lead.
By the end of the hour, Carins has tracked down the person she believes is the now-ex-girlfriend of the man who killed her child, Lena (Mia Tomlinson). Under her writer's guise, she ingratiates herself with the innocent thing, gets her drunk, and breaks into her phone, discovering the contact info for "George," the same name as seen on the vanity license plate on a speeding roadster roaring around the island. If the cops don't help, she'll do it herself.
Except, of course, there is one cop who hasn't let it go. Strangeways even makes a point of checking in on Carins when he heads to London for the memorial service for his deceased colleague. So now we have someone who knows that she's left it all behind, with an apartment sitter who is long-term keeping up appearances in London, while Cairns plots her way to killing the man who took her only child from her. Hopefully, in the next episode, we'll meet him.