The book is a travel journal and diary for Shenarah Ilihorn, a high elf wizard from Neverwinter. The early pages describe her departure from Neverwinter, and her travels across the sword coast.
Midway through the journal, she describes meeting People/Ammon Jerro, a human warlock. She describes him as “…
physically impressive man made all the more powerful-seeming by his considerable charisma, commanding voice, and determined manner.” Through the pages, Shenarah details the partnership between herself and Ammon as they delved into secrets of the lower planes, seeking better understanding of devils, demons, and denizens of alternate planes of existance. Their work together deepened their partnership, which grew into a bond of love and devotion.
Continuing your search through the journal, you pick out some passages:
2nd day of Hammer - 1390 - “Ammon has always been powerful, but he has finally shared his secret. His power was initially drawn from the contracts he made with the pit fiend Koraboros. A promise of service and loyalty in return for power. I knew that his power came from outside our plane, but his contract with the fiend worries me. Such creatures by their nature corrupt even the best of intentions.”
20th day of Uktar - 1396- “Ammon is always circumspect about how he first met Koraboros. A secret tragedy he holds close to his heart. I know that he has strained against the contract under Koraboros. He seeks greater power, and freedom from the influence of the fiend.”
18th day of Ches - 1400 - “Our plans are coming closer to fruition. Ammon’s spell of planar binding is almost ready. We have been so very careful to avoid alerting Koraboros of our plans. A way to release Ammon from the chains of servitude, and more. To reverse the roles of master and slave, of guard and captive. We must be careful, but swift.”
5th day of Kythorn - 1405- “He assures me that all is under control, but I have begun to see changes within him. His patience, while always limited, has become even more strained. We are so close… so close to achieving our goals and securing his freedom.”
12th day of Eleasias - 1409 - “It is done! After decades of toil and labor, our fate is in our hands once again! So much preparation and plotting. Hidden motivations, subtle manipulation of the fiend, all for today. Our trap, spring the instant Koraboros thought he tasted victory. Koraboros, trapped in our plane, bound to the haven.”
1st day of Eleint - 1409 - “With the sealing of Koraboros, we must secret away the keys to his freedom. They must be far from his prison, as their mere presence can be seen to weaken his bindings. Though the fiend is bound, his influence reaches beyond the bars of his prison. We must ensure that he never get the chance at freedom, lest his vengeful wrath be fully unleashed.”
The last entry in the journal reads as follows:
6th day of Uktar - 1409 - “I carry a piece of the ritual, one of the binding keys to the dwarves of Axeholm. They have been friendly to us in the past. I will secure their aid in protecting this secret. If fate is with us, their fortress and walls will forever seal the fate of Koraboros.