During the coldest winter ever, George and Gracie land in Menlo Park, New Jersey, 1879 - near Thomas Edison's famous laboratory. Mr. Edison has just invented a long-burning light bulb, but he's keeping a huge secret: he's also discovered time travel. In fact, he built his own time machine. The kids get an even bigger surprise when a young Mr. Crowe walks into Edison's laboratory - as his assistant! The older and dangerous Mr. Crowe is sneaking around Menlo Park, too, with plans to destroy the time machine. If he does, George and Gracie will be stuck in 1879...forever. The twins need Mr. Edison's help. But can they stop Crowe in time?