The demonic tome, or The Confession of Ellemar, is found during the Shadow of the Storm quest. It's the final confession of a Saradomin mage who, while studying some of the dark arts, summoned a powerful demon from another realm.
One of its most important uses is that it contains a chant that is needed to "summon" the demon Agrith-Naar (but actually returns him to his realm) during the quest. The chant differs from player to player, but the words used are: Tarren, Caldar, Camerinthum, Agrith-Naar, and Nahudu.
The same chant spoken backwards truly summons the demon at the end of the quest.
After the quest, this book can be found on the shelves in Player-owned houses.
I know that it is too late to prevent my execution, and I do not dispute the letter of the charges against me. I did read forbidden books, and I did perform unholy rituals forbidden by the Church of Saradomin. But I hope to show by this account that I did not blaspheme against holy Saradomin but rather acted in his spirit. For as long as we know, those who worship Saradomin have fallen prey to demons, both those that are summoned by dark wizards and those that live wild in the desolate north. But even priests of Saradomin know little about these creatures, for all knowledge of them is suppressed by the Church. Should we not know our enemies? IF we were to read the tomes of demon-lore, and yet keep the light of Saradomin in our hearts, might we not find new and better ways to fight these beasts?
It was with that thought in mind that I performed the actions for which I have been convicted. And, as I read about the various types of demon, I did indeed strike upon a way that unholy magic could be used for a holy purpose. Not all demons are most dangerous when they are on our plane as physical beings. There is also a more subtle demonic influence that pervades our world, with demons working behind the scenes to cause natural disasters and accidents. The chief among these demons is Agrith-Naar.
If Agrith-Naar were to be removed from his own dimension he would be unable to work his magic on the world, and so I came to believe that summoning him would not be an evil act, but a good one. Therefore I secretly studied the forbidden books and conducted magical experiments, until I had discovered the means by which Agrith-Naar could be summoned. The process of preparation was complex, but the most important part was the construction of a sigil of the demon out of silver. The final act was for eight persons, each holding such a sigil, to recite the following incantation:
‘<The reverse of the incantation that Denath provided you with>’
The ritual was a success, and the great demon Agrith-Naar appeared before us. We had prepared a magical cage, and with difficulty we imprisoned the demon. However, we were unable to destroy him, though we tried every physical and magical means.
Furthermore, the magical cage was weakening, and we feared it would not be able to contain him for long. Therefore we decided to
[The last pages of the book have been torn out]