A casual fishing excursion becomes the catalyst for a criminal investigation after a tragic discovery in a coastal inlet. A methodical police inspector pursues the case through careful on-site experiments, the tracing of a mysterious crate, and repeated enquiries that move the inquiry between rural moorland and London. The narrative emphasizes patient, technical detection: gathering physical evidence, checking alibis, and following documentary leads that reveal blackmail and an accomplice. Procedural diligence and incremental breakthroughs drive the plot to a final resolution that identifies the guilty parties and explains their motives.