The Dragon's Maze is the big secret, Jace spent so much time on during his stay on Ravnica. Now the riddle is solved, thanks to the Izzet and their leader Niv-Mizzet, Dracogenius. A certain Ral Zarek, a high-ranking Guildmage of young age, used the notes of Jace Beleren (and the help of his assistant Skreeg) to figure out that at the end of the maze, at the forum of Azor, lies an unbelievable power. What exactly this power is, is not known, but we can expect it to be quite impressive.
The Implicit Maze itself was created by one of the initiators of the original guildpact, Azor I. and was supposed to serve as a peaceful remedy for a time in which the guildpact doesn't exist anymore. That time has come and so the Maze, consisting of mystical Mana paths and leylines, which drag across the city, especially through the ancient guildgates, that accomodate Magic themselves, manifests.
Niv-Mizzet uses the discovery of Ral Zarek by starting a competition. Therefor each of the ten guilds should send one champion to the transguild promenade from where they can try to solve the puzzle of the labyrinth.
Of course, they have to invade other guilds for that and equally given are those only marginally interested in supporting someone else, as the prize is quite compelling. To quote Niv-Mizzet: "One being...will rule the guilds of Ravnica".
Unsurprisingly the ten guilds delegate their finest warriors:Azorius: Lavinia of the Tenth
Who wins this strange competition and which danger lie behind the ancient guildgates? Those two questions have to be answered as has the one, who will rule Ravnica in the end. After all neither Niv-Mizzet nor Ral Zarek are known for their honesty and as the people who discovered the Maze in the first time, I would be very surprised if they don't have an ace up their sleeves.
And then there is Jace, of course. Jace Beleren not only killed his time on Ravnica by examining the Maze, but he also freed his old friend Emmara from the hands (and teeth) of Mirko Vosk. Thereby he had to tangle with other guild champions, especially Exava, a Rakdos Blood Witch. She was close to defeating Jace several times. His last rescue Mr Beleren owed to none other than Lazav, master of House Dimir, whose plans are as mysterious as Lazav him(?)self and so we can be excited, too, which role Jace has to play.
All those riddles will be solved in a few weeks, while tracking through the Implicit Maze at the Prerelease of your choice.