It's appropriate that the ghost of Arthur Conan Doyle should loom over Colin Cotterill's novels. The latter's hero, aged coroner and medium Siri Paiboun, certainly plays host to enough spirits as he investigates murders in Communist-ruled Laos in the '70s. In Disco for the Departed, his third adventure, Dr. Paiboun is troubled by both the death of a Cuban nurse and the deceased's continuing love for pop music (or, as Paiboun describes it, ''this wailing of tortured Americans''). While undeniably soft-boiled, Cotterill's writing is both evocative and educational. Who knew, for instance, that eating bats is good for you?