You need to mindread Erlking. After that you can read the book he was thinking of in the bookcase on the other side of the room (on the right, to the far back). You may need to scroll down the list of books.
If you can not get into his room, you need to take the elevator platform down to the morgue level to get the key.
You need to take over the battle tower in order to be able to transform into a dragon, which will let you get to the place in the fjords where you need to go to lower the barrier blocking off access to the rest of that area.
There is a warning in-game, but once you get the summoning contract, finish everything else in Broken Valley and Sentinel Island before proceeding up to the summoning chamber. One quest in each region can or must be left until later: rescuing some miners in the quarry tower and retrieving some treasure from a boat in a tree (though you may want to use the item yourself, rather than complete that quest).
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