It is said that sometimes the nobles of a Faerie shee decide to send a double of a human inhabitant of New Troy to replace the original. It is not known to what purpose they do this, but it is believed that, every so often, a 'real' person is spirited away somewhere and replaced by such a wraith, or fetch. The fetch is like the original in every way, completely identical, with all of his or her knowledge, character traits, and flaws. Underneath it is a cipher, and a malevolent one at that, but even close family members will be unable to tell there is anything amiss.
Everybody in New Troy knows, therefore, that if one sees one's double or twin - only ever when one is alone; only ever when it is dusk or early morning; only ever in some isolated spot where no cry for help will be heard - it can only mean that this is a fetch and shortly one will lose the life one had, and be replaced by this malicious being. It will soon be living as you did, amongst your friends and loved ones, and all you know of your fate, whatever it is, is that you will never see them again.