My old master was a collector of things. Skeletons, staves, and priceless artifacts. The most prized of which were the helm and staff of Mannimarco himself, the King of Worms.
The old master was also a collector of apprentices, which in our trade are even more dangerous than the artifacts. He was aware of my ambition, and where it would end. He knew I would steal his artifacts and kill anyone who stood in my way, himself included.
So like any good necromancer would do, he made sure his trap would ensnare me even beyond the grave.
The doors are blocked by some kind of invisible ward, but there must be a way to remove it. The master was nothing if not circumspect, and he would've left himself an out were he to fall victim to his own trap.
In fact, I think he aimed to make a game of it. His final words to me were, "start with the map."
I've tried to make sense of the clue, and have made some progress. The flags seem to represent the torches. I just have to remove the right ones.
This book was included in Gallows Hall from the Creation Club