monk reluctantly agrees to accompany his long-suffering assistant, Natalie, to France, and then shocks her by announcing that he wants to visit of all things the sewers of Paris. Not his usual cup of (milk-free)tea. But the historic underground maze of pipes and tunnels is famous for making the city of light admirably sanitary, and to monk, that's worth paying tribute. And he can always wear a haz-mat suit for the tour.

The only problems is that Natalie and Monk's explorations lead them to the famed Parisian catacombs, which are filled with ageless skulls and bones. But Monk's sharp eye catches sight of one skull that's not so old-and that shows evidence of murder. The roundabout clues lead them to some unusual suspects including a subculture of people taking a political stand by living only on what they find in the sudder garbage. Solving this murder case will make Monk miserable.