The Ivory Dagger — Patricia Wentworth

When Lila Dryden is discovered standing over the dead body of her irritating fiance with a dagger in her hand, Miss Silver is called in to investigate. What her patience and particular genius uncover is Lila's talent for sleepwalking, the return of her former lover, and the victim's entire staff and circle of acquaintances -- all of whom occasionally wished him dead.

THEY ALL HATED HERBERT

HIS FIANCEE: “I couldn't bear to have him touch me.”

THE BUTLER: “I had given notice. I had had enough.”

HIS SECRETARY: “He told me he was providing for me and the child in his will. He told me, he told me…

THE PROFESSOR: “So I killed Herbert Whitall, did I? What was my motive…besides hate?”