On a return trip from Germany, Monk and Natalie stop over in Paris. They visit the catacombs—a vast, underground cavern in the center of the city, lined with millions of human bones. Monk picks up a skull and announces that the person was murdered. Most of the bodies came from a battlefield, but Monk believes the wound that killed this man came from a modern weapon made in the last few years. He thinks someone hid a recent murder victim among the ancient bones. As Monk starts to investigate the crime, he uncovers another murder that involves a society of “dumpster divers,” people who live commerce-free off the waste of society. It might just be the last straw in Monk’s visit to Paris…