Hamtaro dreams that he and his friends are cave-hams, and they meet a flying hamster called Bo who has lost his magical umbrella, and, without it, he can't make a rainbow or get back home. They go to the village guru (Elder-Ham) to find out where the umbrella is. They end up looking for it on a mammoth, but Bo and Hamtaro are sucked into its trunk! Can the Ham-Hams save them?