Child Ballads
From Tardis Wiki, the free Doctor Who reference
Child Ballads was a collection of folklore ballads by Francis James Child. It contained multiple versions of each story.
The 39th ballad was called Tam Lin. Thomas Laneford believed that Mab kept this book in the Carterhaugh House library because she featured in this particular story.
In 2016, Thomas managed to give this book to April MacLean, hoping she would be able to use it to save him. (AUDIO: Gifted)