A Tower Book is a Book that can be unlocked by collecting Tower Stones.
It is on the top left of the Home screen.
Tower Stones can be obtained by destroying an opponent's Towers.
The rewards from a Tower Book change depending on the League, similar to regular Books.
A new Tower Book is added after a set period of time, and a maximum of 2 Books can be unlocked at a time. When all available Tower Books have been unlocked, the amount of time required until you can receive the next Book is shown.