On “The Sinner,” a woman named Cora Tannetti (Jessica Biel) experiences a sudden rage and stabs a stranger to death in front of dozens of witnesses. The scene takes place on a beach during a sunny day. The setup is so ordinary that the unexpectedness of the act is startling to watch. What follows is a police procedural that focuses on why instead of who. Portraying a killer’s psychological motives without contrived plot twists can be challenging and “The Sinner” is good at keeping them to a minimum. The mystery unfolds at a satisfying pace and Biel gives a solid performance as a troubled woman who is as inexplicable as the violent act she commits.

What we know about Cora pre-murder is purposely limited. Quiet and shy, she is married with a baby son and works for her husband’s tightknit family. She wants more time away from her husband’s parents, who live next door, yet there’s something forced about her marital intimacy, as if she must work herself up to it. She takes pills to sleep. She seems to be a devoted mother. In flashbacks, we learn that she grew up in a repressively religious household. Biel plays Cora using a lot of body language and it’s effective. She reveals Cora to us in small moments, through silences and memories.

Post-murder, Cora is confused and scared and claims she has no idea what drove her to stab a stranger to death. Later, she is seemingly resigned to her fate, which creates some sympathy for her. If we don’t care about Cora as a person, it would be hard to care about why she did it. The viewers’ surrogate for this part of the story is Detective Harry Ambrose (Bill Pullman) who sees past Cora’s crime to the damaged woman she is. His determination to find out what happened to her drives the action.

As a character, Harry is easier to get to know than Cora. Early on, we learn about his sadomasochistic relationship with a local waitress and in contrast to Cora, we’re given more of Harry’s thoughts, feelings and interactions. It’s a good balance that allows us to invest more in Harry and the journey he will take uncovering Cora’s secrets.

Basing an entire murder mystery on why rather than who is ambitious because each step to the final answer must create suspense without the storytelling benefits of pointing to other characters who may have done it. Psychological plot detours sometimes require more patience as we wait for the moment or more likely, piece together many moments, that will lead a character to a future psychic breaking point. In pace and performance, “The Sinner” meets this challenge and delivers a compelling thriller. And unlike most “whodunit’s,” there’s a good chance that the answer to “why” will be much more disturbing.

“The Sinner” is on Wednesdays at 10 p.m. EDT on USA.

— Melissa Crawley is the author of “Mr. Sorkin Goes to Washington: Shaping the President on Television’s ‘The West Wing’” and the recently released “The American Television Critic.” She has a Ph.D. in media studies and is a member of the Television Critics Association. To comment on Stay Tuned, email her at staytuned@outlook.com or follow her on Twitter at @MelissaCrawley.