Lily is an adaptable and resourceful woman who resides with her parents and maintains a quiet local life. Having previously attended an archival studies program in London alongside Martha, she possesses a confrontational nature and a history of decisive, occasionally violent action. She agrees to help Martha investigate Alan's suspicious activities, utilizing her analytical mindset and ability to adopt false personas to track his movements across different states.

Martha is a newlywed librarian who initially marries for companionship rather than intense passion. She lives a quiet life until she notices a malevolent expression on her husband's face and discovers a mysterious stain on his clothing. Her growing anxiety transforms her from an unsuspecting wife into an amateur detective determined to uncover the truth about her partner's travels.

Alan is a traveling salesman who sells math and science-related T-shirts at educational conferences across the country. He presents a public persona of a kind, ordinary husband with a placid smile, yet he remains somewhat of a stranger to his wife. His frequent work trips and vague explanations for his activities prompt intense scrutiny from those closest to him.

Ethan is Martha's former boyfriend from her time in graduate school, initially introduced as a visiting writer. He has a history of manipulative behavior, taking pleasure in corrupting and controlling mild-mannered women. He resurfaces years later in Saratoga Springs, raising alarming questions about his current motives and his connection to Alan's travels.

Henry is a former police officer who transitioned into working as a private investigator. He maintains an ongoing friendship with Lily despite a complicated past where she stabbed him during a previous investigation. He serves as a reliable confidant and offers his investigative expertise when Lily requires assistance.

Josie is a newly married teacher from Woodstock, New York, attending her first professional conference. She maintains a polyamorous relationship with her husband and seeks a sexual adventure while out of town. The mysterious circumstances surrounding her experience at the conference serve as a catalyst for the ensuing investigations.

Travis is Josie's husband, residing in the small town of Woodstock, New York. He maintains an open marriage with his wife and actively posts online to seek information regarding the incident at her conference. He firmly rejects the official narratives surrounding his wife's actions and insists on launching a thorough investigation.

Vicky is Ethan Saltz's estranged sister who lives in New Jersey and recently purchased their childhood home. She holds a deeply negative view of her brother, describing him as evil, and strictly avoids any contact with him or his associates.

Scott is Ethan's estranged brother who resides on Cape Cod. He shares his sister's intense distrust of Ethan, having severed ties with him over a decade ago following a disturbing incident involving his high school girlfriend.

Alice is a tattoo artist currently living in Queens who attended high school with Ethan. She provides crucial insight into Ethan's teenage years, recalling his early fascination with art forgeries and his self-described sociopathic tendencies.

Libby is a local resident of Shepaug who works at a bookstore. She serves as a valuable source of community gossip, eagerly sharing the local rumors and details surrounding the teacher-training conference with Lily.

Detective Cruz is a police officer running an investigation in Fort Myers, Florida. She shares details about a local scam operation targeting convention attendees, providing Martha with valuable context for her search.

Detective Callahan works for the San Diego police department. She assists Martha by sharing evidence details from a crime scene, specifically recalling a distinctive piece of jewelry that connects to Martha's personal life.

Lily's father is an aging man who lives in Shepaug with his wife and daughter. He provides Lily with helpful community connections and speculates about the romantic potential between his daughter and her private investigator friend.

Lily's mother lives with her family in Shepaug and relies on her daughter for assistance. She acts as a point of contact when Lily's friends attempt to reach her at the family home.

Rebecca is a Philadelphia resident with two children from a previous marriage. She lives with her husband and acts protectively of his personal contact information when approached by strangers.

Chris manages the daily operations of an art gallery in Philadelphia. He handles client information and employee schedules, making him a reluctant but necessary source of information for private investigators.

Larry is the only male student in Martha and Lily's graduate program. He develops an obvious crush on Martha during their studies, though his affections go largely unreciprocated.