When the meme was revived, I surrendered twice. My second prompt, from jjpor, was:
A good old classical country house murder mystery, with a twist; nobody had lived in this particular country house for a long time. All the characters are ghosts.
Since this prompt, just like my previous one, centred around ghosts, I couldn't resist putting the two in the same continuity.
Title: Murder at Mallerton
Premise: In the 1930s, Mallerton Manor burned down under suspicious circumstances, killing several people. Their ghosts haunt the ruin to this day, unable to rest until the mystery is solved. And a fatal accident has just added Sally Reade, an innocent tourist from the present day, to their number.