There is a pen in circulation in the city. No one seems to be able to hold onto it for long. It’s always left on a desk at school or loaned and not returned. The pen itself is nondescript: a plain white bic that writes in either black or blue ink depending on whose account of its history you believe. The pen is remarkable in that it is only capable of writing the truth. If something untrue is written with it, the pen will appear to be out of ink.
Locating the pen is difficult, as it moves almost of its own accord, but you can easily locate it by sympathy. Break open a pen of the same colour and rub the ink on your palms. When the pen draws near, you’ll feel your skin begin to tingle, and whoever owns the pen at the moment will leave it in your hand at the slightest pretext. The unfortunate side effect of this sympathy is that the pen’s honesty rubs off on you.
The only rule to observe when using the pen is to never engage in automatic writing, sketching, or any other idle activity. Your hand will be compelled to reveal things your mind ought to hide.