It's a new school year with the same old problems: the school is going to run out of money! But a local engineering competition might just keep them funded for another year. Can Millie and her friends Pearl and Halinka invent a way out of the mess? With some guidance from their eccentric headmistress Miss Bunsen, anything seems possible.

When Miss Bunsen receives a mysterious invitation to compete in a maze adventure for a big prize, Pearl, Millie, and Halinka are excited to put their problem-solving skills to the test under pressure. But even though they're cracking all the right codes, they find themselves trapped in a strange maze-and Miss Bunsen has to give up her book of secrets in order to set them free! Will the girls be able to keep their wits and solve their way out of this...