Casper, Kat Harvey, Wendy and Peter Von Trapp took adventures with the Nutcracker in the Land of Parthenia to battle the evil mouse king.
Once upon a time at Whipstaff manor, Casper and Kat are getting ready for Christmas, so they have to do the Nutcracker story by E.T.A. Hoffman Kat begin to read a story while Casper falls asleep. 10 minutes later, Kat falls asleep as Casper did and Wendy and Peter came in the house and saw Casper and Kat asleep. Then suddenly Wendy and Peter saw too many mice dressed as armor and they are about to do something bad, but the mice guards was leading by the Mouse King who is an orphan because his mother the Mouse Queen had died by everyone hero, Prince Eric.
Wendy and Peter woke Casper and Kat and they see those mice attack their Christmas decorations, the four kids demand those mice to leave them alone, but the Mouse King used his staff to shrink the kids small and he did. Then suddenly, the Nutcracker came to the rescue them and told them to leave the kids alone with his sword. After those mice left, Casper, Kat, Wendy and Peter thank the Nutcracker for saving but they need to get big again, but how? Then suddenly the talking owl came and tell them that the sugar plum princess will help them and he told them that the Nutcracker will take the kids to the Land of Parthenia and she can help break the spell.
Later Casper, Kat, Wendy, Peter and the Nutcracker have going to the Iceland and met a snow fairy and she can help them to get to the Land of Parthenia, she calls her dancers to help them away out to save his lover princess, Casper, Kat, Wendy, Peter and the Nutcracker thanks those snow fairies to find their way out and they made their way to the Land of Parthenia. As they have to made their way to the Land of Parthenia, they met the three gingerbread (resembles to Chris Carson, Holly Jollimore and Jimmy Bradley) and they tell them that the mouse king's armies destroyed their village and then they are lost. They told them that the Mouse King's army have destroyed the village because they're too marshmallow, chocolate and candys too.
Meanwhile at the Mouse King's lare, the mouse guards has bring the news to the king and tells him that the Nutcracker Prince and his friends came to the Land of Parthenia and help the others to save a princess so she can help them to break the curse. The Mouse King was angry because Nutcracker and his friends have to see the three gingerbread children whose are lost and they can help them to save Sugarplum Princess. The Mouse King have his evil plan on Casper and his friends so he orders to them to catch them so they can't find the princess.
Back to Casper and Friends, they see those mice trying to catchers them but they are being rescued by the Three Ghosts Musketeers. But the Three Ghost Musketeers (resembles to the Ghostly Trios) names are Pierloth D'Artigom, Gaston La Bon and Regis Lingot D'Or and they can help Casper and his friends to find the Sugarplum Princess and save the land of Parthenia. But Kat told them that the Sugarplum Princess and the Land of Parthenia are in danger by the Mouse King and they must save her and this land and stop him before they try and destroy Casper, Kat, Wendy, Peter and the Nutcracker too.
The Three Ghost Musketeers take the Nutcracker and the 7 children to save everybody and the land of Parthenia as they figure out how to defeat the Mouse King, Wendy told Pierloth that she had her magic wand to find the Sugarplum Princess and defeat the Mouse King so Pierloth takes her, Casper, Kat, Peter and the Nutcracker to locate the princess, while Gaston and Regis stay with the gingerbread children.
Later Pierloth takes the four children and the Nutcracker to the Mouse King's castle but it's a trick because the mouse guards begin to capture Wendy, Peter, the Nutcracker and Pierloth and left Casper and Kat behind. Casper and Kat really need to rescue their friends but how. Then suddenly the Sugarplum fairies show up and help the kids to rescue their friends and they head to find a way to stop the Mouse King.
The Sugarplum fairies show Casper and Kat the Mouse King's and they have to go sneaking to find Wendy, Peter, the Nutcracker and Pierloth in the dungeon. As they found them, they free Wendy, Peter, the Nutcracker and Pierloth and they have to find Sugarplum Princess. But the Sugarplum Princess told them that she's been trap in minor after the Mouse King vanished Prince Eric somewhere in the other side, but Casper, Wendy, Kat, Peter and the gang rushing to him and defeats him by breaking his staff and the Nutcracker turn back to Prince Eric. When the Mouse King and his men were been try to attack Casper and his friends, Gaston, Regis the gingerbread children came with the armies and fights those mice and they did.
After the war, Prince Eric and the Sugarplum Princess thanks Casper, Kat, Wendy and Peter for their help so they and their town people and creatures are very proud of them, the Sugarplum Princess used her powers to return Casper, Kat, Wendy and Peter back to Whipstaff manor and reformed back to theirs size again. After Casper, Kat, Wendy and Peter returns home from the Land of Parthenia, they are so happy to be home and then Dr. James Harvey and the Ghostly Trios came downstairs and they see the children are awakened and they told them about their adventures and lived happily ever after.