The Empty Chamber - A Celia Swift Mystery

Frederick Hackett was shot behind a locked door, in his run-down terrace flat in post-war Essex. When the landlady found him, both assailant and weapon were nowhere to be found. A baffled police inspector enlists a consultant named Celia Swift, who is said to be 'damned good at this sort of thing.' The Empty Chamber is a game of observation, conversation, and deduction, set inside one room.

I recommend playing in full-screen (little square button at bottom-right).