13. The Pale Horse (1961) — Standalone featuring Ariadne Oliver — 13. The Pale Horse (1961) — Standalone featuring Ariadne Oliver

Choose this for a later-period standalone that initially appears to flirt with the supernatural. Mark Easterbrook drives the inquiry, while Ariadne Oliver appears without serving as the lead investigator.

The pleasure comes from watching ordinary inquiry test an atmosphere designed to feel uncanny. Its distance from the standard Poirot or Marple formula makes it a strong change of pace.