Casper meets Wendy the Good Little Witch, who tells him that he is the only free ghost left who can defeat the evil Kibosh. Wendy uses her magic to open a door that leads Casper into the first dimension, the Medieval World. Casper meets the knight Sir Richard, who needs help with finding five parts of his armor and completing three other tasks to collect parts of the key to enter the cave to defeat the dragons which Kibosh put in charge of the Medieval World. After Casper defeats the dragons the Medieval World is free.
Casper goes back to his house to enter the second dimension, Vlad's Amusement Park. After collecting two parts of a ticket to enter the circus tent, Casper defeats Krank, a giant jack-in-the-box who put in charge of the second dimension. In the third dimension, the Spirit Factory, Casper meets Professor Neutron who had been forced to build a machine that will make monsters for Kibosh. After collecting two parts of a key card, Casper defeats Professor Neutron's arch enemy Doctor Deranged and his robot. Back at Casper's house Wendy is captured by Kibosh then an older witch, Vanessa, who is a friend of Wendy opens the door to the next dimension. To get to Kibosh's Castle Casper has to take a Ghost Ship after defeating its captain, Pegleg Potbelly, who works for Kibosh.