-“The book has made me angry!” -“A rather silly plot” -“PHOBIA ALERT!!!” -“No one acts the way they should.” Judging by these reviews, “Dead Simple,” as it turns out, has been very faithfully adapted by BritBox — the online streaming service co-owned by the BBC and ITV — as an entry into its original programming roster. The plot of the BritBox version is truly insane, apparently much like the book, and it’s only thanks to the solid, empathetic performance of John Simm (“Trauma,” “Dr. Who”) as Grace that things don’t go totally off the rails. (Let’s put it this way, he can sell this line: “A stag night is one thing, but you don’t decide to take a coffin on the spur of the moment.”)

Let’s rewind: “Dead Simple” opens with Grace on the stand, defending why — for a second time — he has consulted a medium to help solve a crime. The woo-woo of it all makes the front page of the tabloids the next day, and Grace’s boss asks him to do his damnedest to avoid public drama for a while. Oooh, you’re thinking — cops and mediums? Yeah, that’s straight out of “Unsolved Mysteries” and pretty bonkers. But wait, we’ve just begun! Grace, of course, does not go gently into that good night. He signs on as an officially unofficial consultant for his buddy Detective Sergeant Glenn Branson (Richie Campbell), to help him solve a missing persons case of a groom-to-be who disappeared on his stag night (aka a bachelor party). It turns out the groom’s friends — and I use the term “friends” loosely — decide to get revenge on his past pranks by throwing him into a coffin and burying him in the woods. Lest you think this is heartless, don’t worry, they left him a straw to breathe through and gave him a walkie-talkie so they can taunt him. One problem: The van the pals are in crashes and they all die. Yes. So here we have the groom buried in a coffin in the woods and supposedly all the people who knew about it are dead. How will Grace and Branson find him? There is something to be mined here about how personal desperation can evolve into professional upheaval. Grace’s wife, it is revealed, also disappeared seemingly into the mist on his 40th birthday, and he must now contend with a perpetual series of What Ifs: What if she’s dead? What if she’s alive? What if she chose to leave? What if she didn’t? In turn, the bombastic lunacy of “Dead Simple” can be seen as a manifestation of the character’s worst case scenario free-floating anxieties. What if, in the hideous world of endless possibilities and no answers, his wife was somehow buried in a coffin and left to die in the woods?

Simm, who never seems unbelievable in all of this abject foolishness, could definitely pull off this kind of simmering-beneath-the-surface acting, but that’s not on the page. If that’s the incisive connection drawn in James’ original work, the adaptation by Russell Lewis (“Endeavour”) doesn’t push it to the forefront enough. Instead each development turns into a chaotic form of “Spot the plot hole.” (Would a walkie-talkie work underground? Would a walkie-talkie work underground in a coffin? Would a walkie-talkie work underground in a coffin that’s under a layer of sheet metal?) As if to balance out the roller coaster of plot twists, the production values of “Grace” are bog standard British crime drama 101 — it looks the same as every cop show produced out of Knifecrime Island since the first season of “Prime Suspect” in 1991. Beachy Brighton, admittedly, a nice change from London, is moody, gray, and the woods are menacing. The consistent shorthand of the scenery is one of the most comforting parts of the genre, frankly, and serves as a through-line as things get more ridiculous. SALLY MAIS Also standard in the genre, but noteworthy here: prickly supporting characters. Campbell is terrific as Branson, who acts as the audience stand-in as he reacts with aplomb to Grace’s more outre ideas and the brazen plot. The resigned look he gives Grace when he realizes they are going to the medium again is the look I had on my face the entire time watching this episode. In addition, credit to the production for hiring Cian Binchy, an actor with autism, to play a neurodiverse character on the show. This is exactly the sort of casting that wouldn’t have happened five or 10 years ago, and it is a positive change that should be lauded. For fans of James’ work — and there are many, all of whom apparently like things that are Grade A bonkers — these episodes of “Grace” will be the fulfillment of a long-awaited adaptation. Finally, more than two decades since the first introduction of Roy Grace, readers can see a series about the beloved character. For the rest of us, it remains a big what if: What if this character, with this trauma, could be placed in a story that was more deftly told? That would be something worth watching.

Grade: C+

“Dead Simple,” the first episode of “Grace,” will be available for streaming Tuesday, April 27 on Britbox. The second episode, “Looking Good Dead,” will debut on May 4. Sign Up: Stay on top of the latest breaking film and TV news! Sign up for our Email Newsletters here.