You click on the McM scroll in the lower aisle of the castle library.
You will need the Library Slip from the stack of books at the Mordred Museum. Get the gold coin from the fountain to pay your way in.
the door that's locked
go to the secret door
In the palace the right door
you have to finish the puzzle then click on the door
you want to arrow the door on top of the castle
the guy at the door fives it 2 you
you trad a piece of paper for the password
use the rope and tjhe code dh h husfvbsufhsuiecdfhf
You have to find the key. (see the related question below)
find a way to
You go through the puzzle door and beat Mordred. (see two related questions)
Into the castle. To follow him, you have to solve the puzzle door. (see the related question)