Stone of Vengeance by Victor Thorpe

Murder and theft in the jungle of Burma during the Second World War have repercussions in Nigeria many years later. Paul Okoro and his beautiful wife Aimie find they cannot help getting involved when a rich chief asks Paul to investigate a strange and sinister letter that he has received. Once again, as in The Worshippers and The Instrument, they find themselves facing danger of the most unusual kind.