From Tokyopop:
Merleawe has left her hometown and moved to the capital city of Viegald to attend wizarding school. On her way to her first day of school, she bumps into a man who kidnaps her and takes her to the castle, where she is charged with an awesome task—impersonating the kingdom’s master wizard! Fearing war would break out if it was known the master wizard, Sylthfarn, was missing, Sylthfarn’s inner circle has decided someone must pretend to be him. Merleawe tells them that she will take the job!

But not only does she lack the ability to cast more than simple magic, she also has no idea who the master wizard was! Unraveling the twisted threads of Sylthfarn’s disappearance and keeping up the appearances of both master wizard and first year wizarding student makes Merleawe’s every day challenging, magical, and amazing!