I once read a book about a group of people who discovered a hidden temple city in a mountain range, where the Incas-the ancient civilisation of Peru- had fled to when the spanish invaded. When this group found the burial chamber of one of the inca high priests, they unleashed a powerful curse upon them all...
A secret MLM (pyramid) company that offers eternal life, but in fact it transfers the life forces of its members to those position "above". If you get high enough, (meaning you get enough new members) you start to enjoy the benefits. Maybe a willing sacrifice is much more effective for the transfer. But no one says, that a suddenly unwilling member, threatening to tell the authorities, may not loose it involuntarily... thus start people to vanish, and aged corpses are deposited somewhere safe.