It is unclear how much of the contents of the book were discovered or developed by Gaius and how much came from other sources. For example, the book contains a spell capable of bringing inanimate objects to life, which Merlin mastered on a granite statue of a dog before performing on the magical shield of Knight Valiant (Valiant).
The book also includes instructions for curing magical diseases, which Merlin used to heal Gwen's father when he was infected by a plague that struck Camelot. The book was nearly discovered by Prince Arthur Pendragon during a kingdom wide search for evidence of sorcery when Gaius informed Uther that the plague's origin was magical in nature. Merlin later used the book to determine how to defeat the Afanc that had caused the plague (The Mark of Nimueh).
- Merlin learnt most of the spells he's mastered from Gaius' grimoire.
- Gaius has had the grimoire since he was young.