Three Earth children build a rocket ship and head for a planet that turns out to have new friends and wondrous pink unicorns. The children are unhappy that the residents of Pink Unicorn Planet don't seem to care that their unicorns are slowly becoming fewer and fewer because they know that animals on their own planet have disappeared and many are in danger of disappearing. The children decide to help their new friends come up with ways to save the beautiful unicorns while there is still time.