Cordelia is a 22-year-old former secretary who recently inherited the Pryde Detective Agency. Raised by an itinerant father who thwarted her educational ambitions, she is accustomed to scraping by on very little. She relies on her sharp intellect and the investigative protocol taught by her late partner to prove herself in a male-dominated profession.

Mark is a 21-year-old former Cambridge history student who abandoned his studies to work as a gardener. He recently died by apparent suicide in a rustic cottage on the Summertrees estate. Cordelia pieces together his life through the tidy, ordered environment he left behind and the accounts of his friends.

Sir Ronald is a famous microbiologist who operates a large, expensive laboratory out of his home. Born to a poor family, he achieved wealth and prestige through his marriage and his scientific success. He hires Cordelia to investigate the reasons behind his son's sudden death.

Miss Leaming works as the personal secretary and assistant to Sir Ronald Callender. A former English teacher, she manages many of Sir Ronald's affairs with cool efficiency. She actively opposes the investigation into Mark's death, arguing that the young man's privacy should be respected.

Bernie is a former police officer who opened an unsuccessful detective agency after being dismissed from the force. Following a cancer diagnosis, he takes his own life and leaves the failing business to his young partner. He passes down investigative techniques he claims to have learned from his former police supervisor.

Dalgliesh is a Chief Superintendent with New Scotland Yard. Although he does not actively participate in the early stages of the investigation, his methods shape Cordelia's approach. He is the standard against which Bernie measured his own police work.

Chris is an orphan whom Sir Ronald took in as a teenager. He functions as a laboratory assistant and general aide at the Callender home. He acts as a loyal subordinate to his employer, running errands and managing logistical tasks for the household.

Gary is an autistic boy living near Cambridge. Mark befriended him and regularly spent time babysitting him. His relationship with Mark serves as a point of philosophical debate among Mark's university friends regarding the value of human life.

Major Markland is the owner of the estate where Mark worked as a gardener. He accepted Mark for the position after a brief check with the young man's former university tutor. He views his employees functionally and maintains little curiosity about their personal lives.

Miss Markland lives with her brother at Summertrees and discovered Mark's body. She harbors deep resentment toward younger generations, frequently expressing bitterness about their perceived lack of discipline. She spends significant time around the cottage due to memories of her late fiancé.

Sophie is a university student and part of Mark's close-knit group of friends. She dated Mark for about a year and often engaged him in intense philosophical debates. Despite their past intimacy, she admits to feeling she never truly understood his inner motivations.

Hugo is Sophie's brother and a student at Cambridge. He adopts an aristocratic, lightly ironic demeanor when discussing serious matters. He acts as the unofficial spokesman for his friend group, deflecting Cordelia's questions with polished charm.

Isabelle is a wealthy French student studying at Cambridge. She possesses a deep appreciation for fine art and hosts social gatherings for her peers. She views Cordelia's profession as highly inappropriate for a woman and attempts to buy her way out of the investigation.

Sergeant Maskell is the local police officer who handled the immediate aftermath of Mark's death. He acknowledges certain physical irregularities at the scene but adheres strictly to tangible evidence over speculation. He permits Cordelia to take possession of the items left behind.

Evelyn is Sir Ronald's deceased wife and the daughter of a wealthy landowner. She died when Mark was an infant, leaving behind a significant inheritance for her son. Her family background provided the financial foundation for her husband's scientific career.

Mrs. Goddard was the nanny to Evelyn Bottley and briefly cared for the Callender household. She possesses deep institutional knowledge of Evelyn's family history and Sir Ronald's early years. She holds the key to a message left behind for Mark upon his coming of age.