In this novel, P. D. James features the Scotland Yard inspector Adam Dalgliesh the frequent protagonist of her crime novels. Dalgliesh is a memorable figure in this genre because he is the antithesis of the hard-boiled detective. In addition to being an astute, persistent detective, Dalgliesh is also a published poet. James shows that the sensitivity that goes into Dalgleish’s poetry actually makes him a better detective because it supports his insights into the human soul and psyche, which contribute to his solutions. Relentless in his pursuit of the killer, Dalgliesh nevertheless sometimes suffers from understanding the nature of evil. A tall, thin man in his forties, Dalgliesh grew up the son of a minister. A childless widower who lost his wife and baby in childbirth, he is now in a relationship with literature scholar Emma Lavenham.

Kate Miskin and Piers Tarrant are Metropolitan police detectives who work on the case. Dalgliesh is their supervisor.

Most of the other characters are associated with the Dupayne Museum, of which the titular room is a part. The body of the murder victim in the case that Dalgliesh is investigating was found in that room. A private museum in a wooded area of London, its secluded location figures into the plot.

Three siblings of the Dupayne family are the museum’s trustees, according to the will of its founder, their late father. They have different attitudes toward operating the museum, which is a financial burden: keep it open or shut it down. Marcus and Caroline want the museum to stay open, but not necessarily for philanthropic reasons.

Caroline Dupayne is the assistant principal of a prestigious private school. She lives rent-free in a well-appointed apartment in the same building as the museum. Her interest in keeping it open, Dalgliesh discovers, stems largely from protecting her secret life, which involves using her apartment for illicit sex parties that include British nobility. This seems an adequate motive for murder.

Marcus is the sibling most invested in the museum as an institution. Having just retired from a government bureaucratic post, servant, he has the time to invest in the museum and wants to play a more active role in its administration.

Neville, the first victim, is found burned in his car. The eldest child, a psychologist, Neville had wanted to close the museum, largely for financial reasons. He saw that the money would be better applied to family goals, especially assisting his daughter.

Other characters work at the museum. James Calder-Hale, the curator, wants to insure that the museum continues after he dies of cancer. He has a background in the British intelligence service. Tally Clutton, the custodian, lives in a cottage on the grounds. Muriel Godby is the receptionist; she is fiercely loyal to Caroline, for whom she previously worked at the school. Ryan Archer is a part-time handyman.