Each guardian was to protect their burden with their lives and as a final act, fill the key with their own blood and pass it on to next one worthy enough to carry it. Down through countless eons, innumerable souls have done the best they can, but now only one key remains.
Tales From The Crypt Presents: Demon Knight- Key (clipped to polyvore.com)
One night in a remote country tavern the party meets a stranger. Half starved and nearly half mad, they catch him trying to steal the party's (transport, cash, etc). Soon after, a handsome stranger appears, calling himself a Collector and claiming that the stranger has stolen something from him.
All they have to do now, is survive until sun up...Watched Demon Knight over the weekend and realized that it would make a pretty decent one-off scenario in any game with supernatural elements. The problem might be what to do with the Key at the end of it all if the GM does not want to make it the focus of a long running campaign with the party running from Billy Zane the whole time. The solution to this of course would be Jayda, the bar's spunky young barmaid.