Thirteen-year-old Milos is fascinated by magic and loves to read about it from the illegal spellbooks he keeps under his bed. He dreams about how his life could be different if his father, Lord Andrik, hadn't banned magic in the city of Anadel. Then, Lady Keren from the city of Breen comes to visit the palace, and Milos meets her mischievous son Caleb. After watching Caleb perform a magic spell from one of Milos's books, Milos is curious to try the spell himself.

Milos's father, Lord Andrik (the king of Anadel), has banned magic from the city for good. This is not a very good thing in Milos's opinion because he simply loves everything to do with magic. He loves it so much, in fact, that he has two forbidden spell books stashed away under his bed. When Lady Keren and her son Caleb from the city of Breen come to the palace to visit, Milos is thrilled to have someone his own age around for a change. He is so thrilled that he foolishly decides to show Caleb his illegal spellbooks.

Forbidden Spell is a book about a boy who tries to recreate a spell he saw, and it goes all wrong. Milos, the boy, is the son of a ruler of a city. In this city, his father has banned all magic because it upsets the balance of the city. However, when Caleb, a boy from another city, shows him a bit of magic, he gets excited and tries to recreate it when Caleb is not there. However, things go horribly wrong. Can Milos fix it? Or will he destroy his city?