Jim Henderson is one of six guests summoned by the mysterious Edwin Carson, a collector of precious stones, to a weekend party at his country house, Thrackley. The house is gloomy and forbidding, but the party is warm and hospitable except for the presence of Jacobson, the sinister butler. The other guests are wealthy people draped in jewels; Jim cannot imagine why he belongs in such company. After a weekend of adventure with attempted robbery and a vanishing guest, secrets come to light, and Jim unravels a mystery from his past.