Background
House Dimir is a guild of secrecy, manipulation and underhanded deals, a shadowy organization operating behind the scenes to twist Ravnica to its own ends. The current guildmaster is Lazav. Many House Dimir members work as messengers or reporters and are often employed by the other guilds or the guildless for these purposes.
For a long time. the guild officially didn't exist. The Ravnican people generally believed that there were only nine guilds and that if there ever was a tenth, it had dissolved thousands of years ago. The name Dimir was not known by most people and those that did know it believed it to be a myth, children's story or a paranoid conspiracy theory. This misinformation was actively propagated by the Dimir themselves as a method for avoiding suspicion. The Guildpact's spell was finally broken when Agrus Kos arrested the parun and guildmaster Szadek, which exposed him and House Dimir to the public.