Rainbow Tinseltail and the other students at Sparklegrove School for Unicorns are excited when a brand new unicorn, Sunny Huckleberry, enters the school, but Sunny does not know what his special magical power is, and the thought that he might not have any power at all is making him unhappy. Rainbow (whose power is granting wishes) is eager to help him--even though he does not seem to want her help.