Nicky is a young professor and expert in detective fiction who travels to California to write the private memoirs of a famous author. She is left-handed, naturally empathetic, and possesses an encyclopedic knowledge of mystery plots that rivals her new employer. Though generally soft-hearted, she boxes to stay in shape and refuses to back down from physical confrontations or intimidating individuals.

Madeleine is the adult daughter of Sebastian and Hope Trapp. After withdrawing from law school, she moved back into the family mansion, where she attempts to write screenplays but mostly isolates herself. She is fiercely protective of her ailing father and deeply suspicious of outsiders probing into her family's dark history.

Sebastian is a charismatic and wealthy bestselling mystery novelist. He is suffering from kidney failure and hires Nicky to pen his memoirs before he dies. For twenty years, he has lived under a cloud of public suspicion regarding the unsolved disappearance of his first wife and son.

Diana is Sebastian’s second wife, a beautiful English woman with a conservative, modest demeanor. Originally employed as a social assistant to Sebastian's first wife, she eventually married him after losing her own husband and unborn child in a tragic car accident.

Freddy is Sebastian’s nephew and Simone's son. He often runs errands for the family and assists his uncle with medical appointments, though his efforts rarely earn him respect. He struggles with feelings of inadequacy and a substance use disorder, hiding his resentment behind a goofy exterior.

Hope is Sebastian's first wife, who mysteriously vanished twenty years ago after being dropped off at a liquor store on New Year's Eve. Known through flashbacks and videos, she is remembered as a fierce defender of her sensitive son, frequently clashing with her husband over his harsh parenting style.

Cole is the missing son of Sebastian and Hope Trapp, whose disappearance two decades ago remains unsolved. Described through diaries and home videos, he was a sensitive child with dyslexia who loved making origami butterflies but faced severe emotional abuse from bullies and his father.

Simone is Sebastian’s sister-in-law and the widow of his brother, Dominic. She has an imposing personality and remains heavily involved in the Trapp household. She harbors a lifelong infatuation with Sebastian, causing friction within the family.

A pale, blond English man introduced as a friend of Freddy's. He takes Nicky sailing and shows a keen, almost invasive interest in the Trapp family's history and the unsolved disappearances.

Sebastian's former research assistant. He offers Nicky a grounded, less romanticized perspective on Sebastian's character and the intense bullying Cole endured from his father.

A blue-haired police detective who originally investigated the disappearance of Hope and Cole Trapp. She retains a sharp interest in the family, believing they conceal significant secrets.

A serious, young police detective who partners with Detective Springer. He becomes involved in the unfolding events at the Trapp mansion as new mysteries arise.

A former family friend of the Trapps. He wrote a cruel, tell-all book about Sebastian and Hope following the disappearances, which severed his ties with the household.

Sebastian’s deceased brother, Simone's husband, and Freddy's father. He was killed in a hit-and-run accident years ago, but prior to his death, he was a reliable source of support for Sebastian following the disappearances.

Watson is the traditional name given to all the Trapp family's pet dogs. While past versions are preserved in the attic, the current living Watson roams the mansion and shows a distinct preference for certain guests.