To study the Sun, Mum needs Cosmo and Dad to set up three Solar units on Mercury, the closest planet to the Sun. With no time to spare, Dad and Cosmo take the Moon Buggy while Lifter helps out carrying equipment. Before long, Dad and Lifter find themselves locked in a fast and furious race across Mercury. Cosmo finds that they will have to work together if they are to make their way over the many craters on the hot surface.