There's a statue of him on a column near that bookshelf. The statue has a big purse (players need to ask)

'''Action : Press on the purse''' It unlocks the secret door.

The book shelfs get closer and closer and there's an army of hands with chainmail (he Disguised people as templars)

'''Action : Some smart way to pass through for each players or they get Wounded'''

Someone disgusied as a demon

'''Action : unless Combat (monster) need some smart way to take him down'''