Here's a written guide:
*Although you kill Robert on the evil playthrough and take it from him, it did not work for me. I had to do the ultimate good playthrough.
1. Will need to do all good deeds, and only good deeds in a playthrough.
2. Help all the soldiers in the cities.
3. Will need to fight with/help Tancred, including clearing all 3 evil bases.
4. After the third base, you need to go to the bottom left of the map to confront Robert.
5. Enter the castle, stand in the center of the screen, and kill waves of skeletons with the long range magic blast.
6. A soldier will kill Robert, and you just have to grab the book.