[Kunic]

Mysterium Xarxes

For this next quest, Jauffre sends you back to the Imperial City to check
up on Baurus, the bodyguard who helped you at the start of the game.

Fast travel to the elven gardens district, and go to Luthers Boarding house
where he has his current residence. Inside you'll find him seated at the
bar.

Rather then a warm welcome, he'll instruct you not to say anything but to
simply sit down next to him, do so and he'll mention someone sitting
behind the two of you might be a spy.

As instructed, wait till Baurus get's up, then see the other person
following him and follow the other person. A short fight follows, make
sure Baurus survives. Speak to him to learn the attacker is part of the
Mythic dawn cult.

Baurus suggests you investigate further on the book you find on the
attacker's body, and suggests you speak to Tar-Meena at the arcane
university. She's usually found there in the lobby of the arch-mage's
tower.

Speak to her about the book and she'll mention you need all 4 books to
figure out the next clue, she gives you the second part and instructs you to
go to the first edition bookstore in the Market district to find the third
part.

Once you speak to the shopkeeper there you'll find he does indeed have
the book, but is holding it for someone. You have several options here,
the first is getting the disposition of the shopkeeper over 70 and he'll sell
you the book rather then wait for the other customer, I don't recommend
this as you need the other guy (Gwinas) anyway.

Second is either pickpocking Gwinas for both the book and a note on a
meeting he's arranged to get the fourth book, and killing him for that
same information is also an option btw.

There's also a peacefull solution though, Follow Gwinas back to his room
at the Tiber Septim hotel, confront him with the knowledge that you
know he has that book and tell him the mythic dawn was behind the
murder on the emperor and he'll hand over both the book and the info
without a fight.

Once you have both, speak to Baurus once again, standing outside of the
boarding house this time, and he'll ask you to follow him to that meeting
right now. Be prepared as you'll face three mythic dawn assassins.

Follow baurus into the sewers, and fight your way past another few rats
and mudcrabs and such and you'll reach the place just outside the room
where the meeting is scheduled, here Baurus asks you if you want to be
the one to go in, or if you wish to be the backup, choose and either go in
through the door, or up the stairs. Either way, the cultists come in, speak
for a bit and then attack.

Kill them and on the body of Raven Camoran you find the fourth and last
book of the series. Baurus will mention taking off for cloud ruler temple,
and you're left on your own to solve the riddle of the four books.

If you're not sure, or want someone to tell you, simply speak to
Tar-Meena 4 times on 4 different days and she'll give you the clue. It's not
that hard however, simply put the first letter of each paragraph next to
one another and you get a special sentence:
Green emperor way where tower touches midday sun

Basically, this means go to the green emperor way right there in the city
(it's the road around the palace), wait untill noon and then look at the
surface of the only unnamed column in there. A map will light up and
clicking on it will give you the location of your next quest; Lake Arrius
Caverns.

No need to even report back to Jauffre, though you can if you so wish.