Irene's family has moved to Evreux, in Normandy. An unknown woman approaches the girl and, after saying some incomprehensible phrases about the danger her mother is in, mysteriously disappears. This is only the beginning of a series of disturbing and strange events that Irene, Sherlock, and Lupin will face. The three friends will find themselves in front of a secret crypt in the depths of Paris and will search for an ancient relic of immense value...