British author Sedley (The Weaver's Inheritance; The Goldsmith's Daughter; etc.) offers a vivid picture of day-to-day life and politics in 15th-century England in her latest mystery featuring her peripatetic peddler and part-time sleuth, Roger the Chapman. Despite being recently and happily married to his second wife, Adela, Roger feels his "old, familiar restlessness" and sets off in October of 1477 for Plymouth, where he learns of the murder of Oliver Capstick, an elderly recluse "bludgeoned to death in his bed." Master Capstick, a wealthy tradesman, held the purse strings for a profligate great-nephew, Beric Gifford, who is the prime suspect because of his fiery temper and his refusal to marry his uncle's choice. Beric seems to have disappeared after eating the leaves of the Saint John's fern, which certain superstitious souls believe made him invisible. Reports of Beric's being spotted pique Roger's curiosity and prompt him to investigate. Complications ensue when Roger becomes the scapegoat for a second murder and he must help exonerate one of his new friends. A great, black brute of a horse, a swineherd and his mettlesome, obstinate pigs loom large in his wanderings, while a signet ring and a velvet hat provide important clues. A well-laid if drawn-out plot builds to a logical if incongruous ending that should please the faithful and even win a few new converts. (Aug. 26)