Clearly it contains alchemists' lost secrets to creating slimes. But is cursed to gradually turn anyone who reads it into a slime. Which at least one player will obviously try to do. There's some good motivation to complete the quest and/or make one or more players play as an intelligent slime for a while.
[EDIT] Gelatinous cubes, rather. Now I must read the Book of Shame.
Behold! The legendary Book of Shame!