Marzio Montecristo, a fan of crime novels, opened a small bookstore, Les Chats Noirs, in the center of Cagliari, dedicating it to two black cats—Miss Marple and Poirot. The shop is popular, especially thanks to Patricia, a young employee. In the store, meetings of the reading group “Tuesday Detectives” also take place—an initiative that helped solve a real crime last year. Superintendent Angela Dimasé asks them for help investigating a brutal crime, when an unknown attacker attacked a family, forcing the father to choose who to save. The killer was nicknamed the “hourglass killer” because of his cruelty. Will the “Tuesday Detectives” solve the case and stop the murderer?