Nov Lam took the caver of the Class 1 magician's secret book and exchanged its contents with similar books, at first glance the book was read the same but the subject matter was different. The book contains a preamble to the actual book, the content of the subject is different, there is no theory, method, or result.
Nov Lam sealed the book with a layer of explosive magnets. Placed the main explosive in the cupboard. So...when the book was moved far away from the cupboard it would automatically set off an explosion and detonate another explosive in the other cupboard.
In the morning, Nov Lam had replaced the other books on the shelf, but her movements have to be stopped when a cleaning staff arrived. Nov Lam hid behind a cupboard in the corner.
The janitor was shocked to see an empty cupboard shelf.
He immediately ran to find professor Must in his room. Professor Must lived in that building.
