- “And this was found in Gaius' chambers?”
- — Arthur to Agravaine[src]
The Sorcery book is the book that Agravaine planted in Gaius' chamber so that he would get condemned for practicing magic. Later he showed the book to Arthur who was clearly upset of the thought of Gaius betraying him. He later told Merlin while he was showing him the book that Gaius had condemned himself. Soon Merlin found other books like "Studies in Sorcery" hidden in Agravaine's chambers (The Secret Sharer).
A similar book was given to Merlin in the first series in order for him to study the basics of sorcery (The Dragon's Call).