The Girl in the Cellar Unabridged edition

Miss Silver helps a woman with no memory reconstruct a terrible crime.

She awakes in a dark place. A young woman with a shattered memory, she knows neither who she is nor how she came to be in this abandoned house. All she possesses is a faint sense that someone is lying dead at the foot of the stairs. Horrifyingly, she is correct. In the cellar lies a young woman, her body broken, her head split, her life undone by a revolver’s shell. The amnesiac flees and finally has a stroke of luck: She meets Maud Silver. A dowdy governess turned daring detective, Miss Silver sees immediately that something is wrong. She comforts the confused young woman, and coaxes out of her what little story she can tell. The memory of the body sets Miss Silver on a fantastic adventure—the last written by Patricia Wentworth, and one of the most thrilling of them all.

Miss Silver mystery #32 (her last case).