The Varangian Chronicles

There is a shadowy sect of men who call themselves Lampros. They hold the secrets to the undoing of kingdoms and empires. A cask of plague hidden in a a vault under a temple here. Or perhaps a box of ancient codex written in a script only they have learned to decipher. But their pride and joy — a casket so insightfully designed as to only be opened when all three keys are present — has gone missing. The casket is said hold the only written documents on how to prepare a devastating weapon known as Medean Fire. Yet it may hold something far worse.  They will stop at nothing to get it back.