Wealthy crime novelist Harlan Thrombey invites his family for his birthday party. The next morning, he is found dead. Private detective Benoit Blanc is hired to investigate. He discovers that Harlan's family had been alienated and had motives for killing him. However, it is revealed that Harlan's nurse Marta was responsible for his death accidentally. The family turns against Marta, but she is aided by Ransom, Harlan's grandson. As the investigation unfolds, it is revealed that Ransom planned to frame Marta for the murder. In the end, Marta is proven innocent and inherits Harlan's fortunes.

Tech billionaire Miles Bron invites his friends for a getaway on his private Greek island. When someone turns up dead, Detective Benoit Blanc is put on the case. During the COVID-19 pandemic in May 2020, Detective Benoit Blanc is hired to investigate the death of Helen's twin sister, Cassandra 'Andi' Brand. Andi had committed suicide and sent an email threatening to expose evidence that could bring down Miles' empire. Helen believes Andi was murdered and invites Blanc to a murder mystery weekend on Miles' private island. As Blanc investigates, he discovers a web of deceit, betrayal, and a dangerous new technology called Klear. In the end, Blanc exposes Miles as the killer, leading to the destruction of his reputation and the revelation of Klear's dangers.

Benoit Blanc returns in his most dangerous case yet.