When you first received the Bartholomew Medallion, it was only present under certain circumstances, which have not been fully defined at this point. It is now a permanent object in your possession.
When you wear the Bartholomew Medallion, you can harness its powers. The medallion has three charges per day; each ability drains a specific number of charges when it is used. The medallion's charges replenish one minute after midnight, when the new day begins.
You summon a small mouse and send your awareness into its body. You use its eyes and ears to sense the world around it, and you may gently nudge it in directions you would like it to travel. When you activate Surveil, the mouse's eyes flash blue, and you experience a moment of vertigo as your senses shift to its body. The mouse will not risk itself under your guidance, but it will generally travel into any safe-seeming location as you urge. You may send the mouse up to 640 feet from where your body rests, and you may travel with the rat for up to 12 turns. Returning to your own body is as simple as opening your eyes, requiring only a Free Action. When you return to your body, the Surveil ability ends, regardless of any remaining duration. While using Surveil, you are affected by any effect targeting sight or sound in the vicinity of the mouse. This ability cannot be used in the rare domain, such as Keening, where there are no living mice.
As a Partial Move Action, you summon a rat swarm to any point within sixty feet of you. The swarm is full of voracious rats with glowing blue eyes. You designate the swarm's first target, which must be edible to them, and they will attack until it is dead (or devoured). Thereafter, if the swarm survives, it moves on to the next nearest target, as it chooses. The swarm persists for seven rounds, or until it is dispersed by losing all of its hit points.
Touch the medallion and focus your attention on a conundrum in order to gain a flash of insight. In game terms, the DM reminds you of a fact or event that has been forgotten, overlooked, or discounted. If there are no forgotten facts, the DM may, at his discretion, tell you of new information relevant to the condition at hand. The reminder or information will always be relevant and useful but will not be unbalancing to the situation. The reminder can be cryptic, depending on the situation. If Insight is used on multiple days in regard to the same situation, it may or may not result in the same hint.
Any attempt to use the Turn Undead class ability using the Bartholomew Medallion as a holy symbol gains a +2 bonus to success dice.
It seems that the two forces within the medallion are not static. The decisions that you make feed one or the other. When you were stricken by the curse of lycanthropy, your many noble decisions enabled the angelic presence to communicate with you. This entity offered protection against the spreading curse, and the diabolical shift it would introduce into your psyche.
It remains to be seen how continuing to feed the angelic presence--or the demonic one--might manifest in other powers.
The Bartholomew Medallion is related in some way to a package delivered on the morning of Dechan Mackenzie's first adventure with the Heirs to The Missed. The package came from a carriage bearing the heraldry of the Iron Crown of Darkon. An eimssary of Azalin Rex delivered it in the presemce of the Kargat vampire Nala-Lyn. The very public delivery bore weight and meaning that could not be overlooked by anyone in the Enclave. The package itself, once opened, seemed to be empty. However, soon after, Dechan found that he had a strange guardian and advisor named Bartholomew, an old man of apparently encyclopedic knowledge.
In the beginning, Bartholomew grew tired after lending any sort of advice or insight, and soon after he retired, Dechan's friends forgot that the old man even existed. The next morning, when Bartholomew returned, it was as if he never left.
On rare occasions, Bartholomew vanished. In his place Dechan could expect to find this amulet. Now, the amulet is a permanent item, unrelated to Bartholomew's presence or absence.
Now, Bartholomew is a permanent fixture in the memory of those who have met him, recalled as a kindly, helpful old man who took an interest in Dechan. Some of Dechan's associates, such as his mentor Labonita, seem to be able to remember Bartholomew only in this way. If any conversation occurs that implies subterfuge on Bartholomew's part, she forgets it soon after.
The medallion is pure gold but at its center is a kernel of concentrated negative energy, pulled from the depths of the Negative Material Plane. Saturated throughout the medallion is a much smaller measure of pure positive energy, delivered out of the Seven Heavens.
It was created through a convoluted process involving divine magic layered over the will of a being of nearly deific power. The process was corrupted, however, introducing the celestial energies.
The priests who were employed in the creation of this item were priests of Orcus, the Lord of the Undead. However, you also sense that someone else--an intruder, but not a celestial--became involved in the enchantment process.
The original purpose of the medallion was to tempt and ultimately corrupt its chosen bearer, Dechan Mackenzie. That purpose was altered before its enchantment was completed, however. Though there was no corporeal presence in its intervention, the intruder managed to alter the make-up of the item, removing intended compulsions and laying the groundwork for other potential abilities.
In recent months, the medallion has changed hands multiple times. It has indeed been in the possession of Dechan Mackenzie. Before Dechan, it was handled briefly by Nala-Lyn, a Kargat agent of considerable power and age. Nala-Lyn received it from Azalin Rex himself, who had received it from a special courier out of the House of Sages. The identity of that courier, however--or his purpose in carrying the amulet--is vague. It seems that the courier recovered it personally, at great expense (monetary and living), to bring it to the Iron Crown so that it could be delivered to Dechan Mackenzie.