Malcolm is a widower and the co-owner of Old Devils, a mystery bookstore in Boston. He lives a relatively isolated life focused heavily on managing his shop and grieving his late wife, Claire. When an old blog post he wrote about "perfect murders" in literature becomes the focal point of an active FBI investigation, his quiet routine is entirely upended.

Gwen is an FBI Special Agent investigating a series of murders that seemingly mimic famous mystery novels. She is fiercely determined and convinced of the connection between the real-life killings and Malcolm's literary list. As she pulls Malcolm into her investigation, she operates with a focused intensity that occasionally conflicts with standard Bureau procedures.

Marty is a former police officer who works part-time as a security consultant for downtown Boston hotels. He frequents Old Devils Bookstore and occasionally shares drinks with Malcolm. Dealing with a failing marriage, he spends much of his time reading the mystery books Malcolm recommends.

Claire is Malcolm's late wife, who died in a car accident five years before the start of the narrative. During her life, she struggled with drug addiction and complex personal traumas that placed significant strain on their marriage. She remains a constant presence in Malcolm's thoughts as he navigates the lonely aftermath of her passing.

Emily is a reserved, bookish employee at Old Devils Bookstore. She manages much of the store's online order processing and often wears skirts paired with literary t-shirts. Though quiet and sometimes shy around Malcolm, she opens up more around her coworkers and the local literary community.

Brandon is an outgoing and talkative employee at Old Devils Bookstore. He is currently pursuing a business degree, which makes Malcolm worry he will eventually leave the shop. He provides a cheerful, energetic contrast to the more subdued personalities in the store.

Brian is the co-owner of Old Devils Bookstore and a successful mystery author known for his Ellis Fitzgerald series. He writes his annual book in a short burst and spends much of the remaining year drinking heavily. His struggle with alcohol makes him a functional but frequently absent business partner.

Tess is Brian's much younger wife, who usually resides in Florida where she runs a jewelry store. As a former publicist, she is confident and socially adept. She travels to Boston to assist her husband during his recovery but quickly seeks distraction from her caretaking duties.

Nero is an orange cat who lives at Old Devils Bookstore. He spends his days entirely within the two book-lined rooms of the shop, enjoying a comfortable routine of interacting with customers and being fed by the staff.

Elaine is a regular patron of Old Devils Bookstore who frequently attends author readings. Despite spending heavily on hardback books, she is widely disliked by the staff for her abrasive, argumentative, and bigoted behavior.

Nicholas is an English professor at a local university and a director of Shakespeare productions. He has a troubled personal history involving alcohol offenses and restraining orders from former girlfriends, making him a subject of interest in the ongoing investigation.

Jillian is a poet and the ex-girlfriend of Nicholas Pruitt. She meets with Malcolm under the impression that he is a publisher, providing him with insights into Nicholas's behavior and their turbulent past.

Eric is a man who ran an artist incubator program in Southwell. He played a significantly negative role in Claire Mallory's life by supplying her with drugs in exchange for sexual favors, making him a source of deep resentment for Malcolm.

Agent Perez is a young FBI agent assigned to the serial murder case. She steps in to interview Malcolm and verify his alibis, operating strictly by the book and maintaining a formal, professional distance.

Agent Berry is an FBI agent who works alongside Agent Perez. He assists in questioning Malcolm about his connections to the victims and his interactions with Gwen Mulvey, ensuring investigative protocols are followed.

Jane is a local mystery author who frequently holds events at Old Devils Bookstore. She integrates herself into the store's social circle through her relationship with one of the employees.

Steven is a former middle school science teacher whose actions left a lasting, traumatic impact on his students. His history of predatory behavior casts a long shadow over the lives of several individuals in the narrative.