The story begins with the apparent suicide of wealthy crime novelist Harlan Thrombey, found dead in his mansion on the morning after his 85th birthday. The Thrombey family gathers to mourn, but the atmosphere is fraught with tension and old grudges. Everyone within the household seems to have a motive for wanting Harlan dead, from his dependent children and their spouses to his cutthroat business associates. On the periphery of the family drama is Marta Cabrera, Harlan's devoted nurse, who appears to have a special bond with the deceased writer.

A debonair private detective, Benoit Blanc, is anonymously hired to investigate Harlan's death. He sifts through a web of lies and red herrings, interviewing the eccentric family members and staff. As Blanc delves closer to the truth, relationships unravel, secrets are revealed, and the façade of the respectable Thrombey family starts to crumble. Marta, inadvertently caught in the investigation, must navigate her own moral compass while under the piercing gaze of the enigmatic detective.