The supplies sent in friendship from the Black Boars to Saint Coinach's Find are being pilfered by imps in the guise of beastkin. Were the imps of the enlightened races and a part of a thieves' guild, 'twould be a different matter, but as it is, this merits death. Find them and dispatch them without further ado.
(Begin by surprising a lightning sprite with a /poke, then slay the glowing figure to acquire luminous crystals. Use these items on beasts to see through their guises.)