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.
Home-bound from a five-month mission, the team is called back into action when the vice president is assassinated and the president-elect goes to ground after his motorcade is attacked. Back at home the women are abruptly uprooted when it's feared their lives are in danger as well, and the resulting chaos reveals a deep secret.