I played Thinking Rabbit's Keyhole Murder, their first mystery adventure game. Thinking Rabbit is probably more known for being behind the original Sokoban, but they've made some well-known mystery adventure games as well, this one not as much compared to their later ones (Meurtre d'un Clown especially, which I haven't played yet).

The game takes place on September 4, 1955 in London. You play a detective who heads out to the villa of famously wealthy man Mr. Wilcock as he has received a note that he will be murdered at midnight. You get there before midnight and keep him safe in his 2nd floor study, when at midnight you hear a gunshot! You look through the keyhole to find him dead! But it's a locked room... Who of the people here committed this murder?

From here you carry out your investigation, finding clues, evidence, hidden passages, etc. to discover the truth. Unfortunately for Keyhole Murder, I can't help but compare it to the other detective game that was released a few months prior, Portopia. Keyhole Murder feels very much in line with the Mystery House (Microcabin one) style of gameplay, though with the added gameplay of getting to interrogate suspects. It's just hard to compete with the best adventure game of that year(at least from the ones I've played so far) and one of the most influential ones ever. Honestly, its mystery is at least constructed in a way that felt like I could slowly piece together some of the things going on, finding evidence and bringing them up with suspects. It's definitely better than Mystery House (both the Microcabin and Sierra ones) as both an adventure game in the former case and murder mystery in the latter case.

The ending is actually the best part, where everything is finally laid out.

Ending Spoilers
The maid did it! She was trying to get revenge for her brother, who Mr. Wilcock murdered for trying to blackmail him. Turns out Mr. Wilcock is involved in lots of shady business. She gets the aid of Mr. Wilcock's son, who was also seeking revenge for abandoning him and his mother soon after he was born and thus not giving him an inheritance. There is also a twist: When you see Mr. Wilcock dead in the keyhole, that was actually a ruse by him. He did that as a trick to escape from his would-be murderer, but alas that fails as he tells his secretary, who he doesn't realize is actually his son. The son and maid end up poisoning the secret mechanism in the clock used to open his study's hidden passage, paralyzing him. His son tried to kill him with a knife, but was too cowardly to carry it out, so the maid had to finish the job.