Arachne (no surname given) is an Assassins' Guild School graduate who on completion of her studies was recruited by Lord Vetinari as a prospective Dark Clerk. She apparently begged Vetinari for a diplomatic posting abroad, to a hotter tropical climate which sustains exotic wildlife of the sort in which she is very interested. Seeing possibilities, the Patrician obliged her with a posting to the Embassy in Bugarup. At the embassy in Fourecks, she is able to indulge her specific interest in the exotic fauna of that continent, most specifically its spiders, of which she has possibly the best collection outside any zoo, or even that of the Natural History Department at the Assassins' Guild School, which also encourages its students to take a deep and abiding interest in the care and welfare of certain species of exotic pets. That is, those species which stalk and hunt their prey, or which combine a hunting instinct with the delivery of toxic venom.
Given her education and her passion for poisonous spiders, it is very possible that Vetinari will be retaining her services so as to arrange a convincing accident for a newcomer to Fourecks, who will, alas, be innocent of exactly how dangerous its spiders can be to the unwary. Since Lord Downey will no doubt receive the standard 50% Guild Tax on the deal, he can be counted upon to be discreet.