After Dad boasts to Cosmo that he could climb the biggest mountain in the whole Solar System, Mum asks him to do exactly that. Dad and a very excited Cosmo must travel to Mars to climb the mighty Olympus Mons on Mars. Don't worry – they have help, in the form of Lifter, a big machine who helps out around the Moonbase. But Dad doesn't want help. He said he could climb the mountain by himself and if he asks Lifter for help, he'll look silly! Cosmo must convince Dad to accept help while exploring the amazing mountain on Mars.