Morse and Lewis investigate the death of Laura Poindexter, an American tourist who is part of an exclusive tour group visiting Oxford. Missing from her personal effects is her jewelry, including the Wolvercote Tongue which she was going to donate to the Ashmolean Museum. The pathologist determines that she died of natural causes, but Morse feels there's something not quite right. The mystery deepens when Theodore Kemp, the Ashmolean's expert on the Wolvercote Tongue, is found dead and Mrs. Poindexter's husband goes missing.…