Grimoire of Unknown NecessitiesEquipment 16
Source Pathfinder #173: Doorway to the Red Star
Price 8,000 gp
Weight light
The cover of this grimoire is bound in a strange crimson, pebbly leather that a DC 40 occultism check to Recall Knowledge identifies as the hide of a rare monster from the distant plane of Leng. The grimoire's spine is bound in copper and a spiral of shifting runes slowly swirls across its surface.
Activate 
envision (arcane, divination)
Frequency once per day
Requirements You're an arcane prepared spellcaster and you have rested but not yet prepared your spells for the day
Effect The grimoire provides you with temporary knowledge of a single spell of the highest level you're capable of casting that you don't already have recorded in it or any of your other spellbooks, chosen by the GM based on their knowledge of the adventure to be particularly useful to you during the upcoming day.
A strange quirk of the tome prevents the spell's knowledge from ever traveling further than your own mind. The granted spell is not only removed from the tome's pages at the start of the next day, but is also removed from any other scroll, spellbook, or grimoire the granted spell is copied into, as well as any other way it might have been learned or copied.
Traits
A rules element with this trait is one-of-a-kind. The DC of Recall Knowledge checks related to creatures with this trait is increased by 10.
DivinationThe divination school of magic typically involves obtaining or transferring information, or predicting events.
GrimoireSpellbooks are useful tools for any magic user to write down incantations and runes of power, but where most spellbooks are nothing more than ink on parchment, grimoires have absorbed the magic of the spells within—magic that knowledgeable spellcasters can use to augment their spells.
InvestedA character can wear only 10 magical items that have the invested trait. None of the magical effects of the item apply if the character hasn't invested it, nor can it be activated, though the character still gains any normal benefits from wearing the physical item (like a hat keeping rain off their head).
MagicalSomething with the magical trait is imbued with magical energies not tied to a specific tradition of magic. A magical item radiates a magic aura infused with its dominant school of magic. Some items or effects are closely tied to a particular tradition of magic. In these cases, the item has the arcane, divine, occult, or primal trait instead of the magical trait. Any of these traits indicate that the item is magical.