As schoolmates Dominique, Eric, Josephine, and Ajay are returning home from their first time-travel adventure at the Smithsonian National Air and Space Museum, they realize there are dinosaurs all over their neighborhoods When they return to the Smithsonian to figure out what's amiss, they see that the National Museum of Natural History is now called The Museum of Extinction, many modern animals have become extinct, and dinosaurs have returned. They travel back in time to the 1876 Philadelphia Exhibition and discover that the nefarious Barris brothers have brought back dinosaur eggs as a new business venture. Enlisting the help of William Foulke, Nellie Bly, and Alexander Graham Bell and using their natural history smarts, our heroes must try and thwart this wicked plot. But the kids' story doesn't end there--something is amiss in the next stop on their Smithsonian tour, the National Museum of American History--so they'll have to work together to save history again in volume three.