I had no idea what The Sinner was when I started watching it. And that is probably a good thing, because it made the opening act all the more shocking and sudden. The show opens on Jessica Biel living a non-descript married life with what appears to be a fairly normal humdrum working husband and a young son. However, it soon becomes obvious that she suffers from some kind of trauma. She needs to take anti-anxiety medication to have sex, and she has the general disposition of a neurotic housewife in late 19th century Vienna.

After the first few minutes had passed I started wondering if this was going to be the show for me. I’m not generally a fan of dramas about the nervous tics of traumatized upper-middle class white people, and when Biel’s character wades out into a lake and sinks under the surface the show goes to great lengths to fill the scene with the slow-moving ominousness of evil jelly. I may have audibly sighed at this point. But then it all turns on a dime, with Biel’s character slicing fruit on a beach blanket one moment and then suddenly and viciously stabbing a man to death in the next.

This is hardly a spoiler. The show is very upfront about the fact that it is a whydunnit, rather than a whodunnit. It is obvious that Jessica Biel has snapped and killed this man. The mystery the show sets out to explore is why she did it. But it’s really the suddenness of that scene that got me invested in the rest of the show. You really think you are watching one thing - some boring character study of disaffected neurotic housewives or something - and then suddenly you are watching something else, which is a woman viciously stab a man to death in front of her own son and a beach full of people.

The rest of the show sets out to uncover the trauma that made her snap. There are some weaknesses in how this is done, but generally the show is pretty good at prodding you along with a series of reveals, and when it gets to the final reveal, it’s pretty satisfying how it was all woven together (maybe because it’s based on a novel, we should expect the plotting to be pretty tight). Like any good mystery, it keeps you guessing. The show is also shot through with pretty good material on Catholic guilt, better than most properties deal with it. Biel is traumatized by a lot of things, not least of which is her upbringing and the way her mother holds her hostage to faith, and that is conveyed quite effectively.

Detective Ambrose, on the other hand, played by President Bill Pullman, is a bit less effective as a character and a story device. He is a cliche through and through, the detective consumed by personal demons. This in and of itself is not a dealbreaker, but this character just fell flat for me. Maybe it was all the gratuitous scenes featuring Bill Pullman engaged in quite graphic BDSM sex acts. The theme of guilt serves as a wafer-thin motivation for him to try and “save” this damaged woman, and uncover the true roots of the trauma that caused her to snap. Never mind that in the real world conclusively demonstrating motive is not a necessary part of a criminal homicide prosecution. And also never mind the fact that nobody, not one single person, ever woke up in the morning thinking “I need more scenes of a naked Bill Pullman being choked during sex by an off-duty female bull rider.”

But those quibbles aside the show works as a pulp thriller and an effective whydunnit. And I think it works as well as it does because the opening is so sudden, so shocking and so violent that you really do feel like you are in Detective Ambrose’s shoes wondering why would a seemingly normal person snap like that? You want to find out just as much as the characters in the show want to find out, and so that really helps sweep you along on the narrative journey. That journey might be bumpy in places, but it speaks to the effectiveness of the opening act that you don’t really mind as you wait for the plot to arrive at a point where it explains that confounding, shocking opening act of violence.