Described as an "origin story", the game follows a young Holmes as he investigates a mystery in his family home on a Mediterranean island after his mother's death.
Gameplay centers on gathering clues, which can be linked together in Holmes' "mind palace" to create deductions. These deductions can be linked together to create conclusions, resolving cases. Unlike previous Adventures games, however, Chapter One will feature open-ended gameplay similar to Frogwares' non-Holmes game The Sinking City. The Mediterranean city will serve as an "open world" divided into various districts, some of which will not be initially accessible. Disguises will be required to access certain areas. The developers hope to give players more control over how the investigation develops, and which leads they would like to pursue. There will be different ways to discover various secrets and events, which can unexpectedly lead back to the central investigation.
The game will also contain combat as an "integral" component. Holmes will be able to use his detective abilities to pinpoint enemies' weak points and quickly end fights. Alternatively, he can use observation to take out enemies without directly engaging with them.
The plot will follow a 21-year-old Holmes at the beginning of his career. Following the death of his mother, Violet, the young detective returns to his childhood home on a Mediterranean island. There, Holmes uncovers a sinister conspiracy lurking beneath the surface in the seemingly idyllic town. Corruption and crime are rampant, and the locals shun outsiders. Holmes will also reacquaint himself with his old friend, the enigmatic Jonathan (called "Jon"), who is described as "definitely not Watson".
- Romano, Sal (2020-05-25). "Sherlock Holmes: Chapter One announced for PS5, Xbox Series X, PS4, Xbox One, and PC".
- Fillari, Alessandro (2020-05-25). "The Sinking City Devs Are Tackling Sherlock Holmes Origin Story In A New Game".