Full Item Description
Two sheets of ordinary parchment, vellum, clay tables, pounded metal or any other material capable of being written upon or inscribed.
If sufficiently detailed and powerful divinations are brought to bear, one may be able to detect a subtle linkage between the two sheets. Those who can see magic could see a faint line joining the two pages.
History
Twin paper was originally conceived to provide the Tyresian empire a means to communicate with it's High Seas fleet. It quickly found use with the Diplomatic Corp and in even more sensitive applications, including use by spies deployed in lands of the many enemies of Tyresia.
A great deal of it's appeal is the simplicity of it's use - all one needs to do to use it is to write upon it. No incantations need be spoken, nor magical energies called upon.
Creation/Fabrication
Preparation of the paper (or any other material) in this manner requires the use of a specially formulated magical paste. The paste is applied to one sample of the material and then the second piece is pressed into it. After leaving them together for 24 hours, the paste will have disappeared and the two materials linked.
The paste is very costly to manufacture, the process requiring magical components equal in value to an ounce of gold per square inch of surface. A batch of paste generally requires about a week of work by a skilled alchemist.
Magic/Cursed Properties
Quite simply, anything inscribed upon one sheet will appear on the other, regardless of intervening distances or obstacles.
Magic effects, however, are not transmitted, so trapped gylphs, curses, etc, cannot be duplicated using this item. The text is replicated, but the magic effects are solely confined to the original copy.
The medium cannot be erased and reused - the subtle enchantments upon it cannot survive such rough treatment.
Uses
Communications
One can assemble two books from a sufficient number of such pages. The books then can be used as a secure form of communication.
Espionage
In the interplay between nations, espionage has always been a tool of statecraft. Those realms with magic have open to them many more opportunities for the application of spycraft.
Apart from use as a communication device, with both users aware of the books properties, it can be used to capture secrets if some of the pages were carefully deployed.
Note paper on an important person's desk could be substituted for this paper, and their notes would then be compromised.
Fraud
Even more creatively, one could have the two pages printed with different contracts prior to enchantment, with the signature line in the same location on each sheet.
Once enchanted, signing one contract would sign the other.
Insurance
'Yes, I destroyed the letter - you saw me do it!'.
Sensitive or important documents could be easily backed up 'offsite', as it were.
Plot Ideas
Most of the above uses immediately suggest different plots. The main ones are:
1. Obtain a member of a communications journal pair to cut off communications or substitute alternate orders.
2. Plant the paper where it would pick up important secrets where used.
3. Drop a supply of the paper to an agent undercover in an enemy kingdom.
4. Prevent any of the above :)