The Royal Assassins guild was founded by Shadow Thief in Mulhouse, Perdan. It's purpose is known only to those who are supposed to be members of the guild. Strangers and uninvited troop leaders are not welcome.
Since the alignment of Mulhouse to Caligus, it is rumoured that the secret society has been relocated to Perdan city. This being only speculation, there is still no information on who or what the society entails.