Genevieve digs up a huge bone in the garden that turns out to be a fossilized stegosaurus' hip bone. The girls are thrilled with the discovery until the Old House becomes a dig site and is invaded by hordes of paleontologists and equipment. Calm is briefly restored after Miss Clavel convinces Lord Cucuface to donate the bone to a museum. But when Genevieve misses her beloved bone and runs away, it is up to Madeline to find her and to lure her back with something better.