Speaking with Silence

Walkthrough
Proceed to Snow Veil Sanctum.

Meet Mercer Frey outside Snow Veil Sanctum
Just outside the sanctum, there is an abandoned camp and a dead horse. Mercer explains that they belonged to Karliah, your quarry.

Enter Snow Veil Sanctum
He then tells you to enter the sanctum. Mercer opens the gate to the catacombs, the one requiring a key, with ease.

Note: Entering the sanctum is only possible from this point on. Prior to this quest, the door was locked and unpickable. Also note that a follower cannot enter the catacombs.

Hoards of levelled draugrs and many cleverly placed traps await. At the east side of a large chamber, up some wooden ramps and along a corridor there is a Model Ship on a trapped pedestal that Delvin Mallory will be delighted to pay for.

Mercer and the Dragonborn then finally make it into the sanctum, where more draugrs and a dragon priest stand in the way. Here a word wall for the shout Disarm can be found. A daunting Nordic puzzle door is easily overcome by Mercer, apparently without even using a dragon claw key.

Find Karliah
Just about to enter the last chamber of the sanctum the Dragonborn is knocked unconscious by a poisoned arrow from Karliah's bow. Partially regaining consciousness, the Dragonborn can follow a discussion between Mercer and Karliah, where it quickly becomes clear that not Karliah killed the Guild Master, but the backstabbing Mercer who then framed her for the crime. Karliah avoids a direct confrontation with Mercer, drinking a potion of invisibility and escaping the sanctum. Mercer is not about to leave any loose ends untied, and stabs the still paralysed Dragonborn without mercy. And so Mercer's betrayal leaves the Dragonborn for dead.

Speak to Karliah
Once the Dragonborn wakes up again, speaking with Karliah will fill in the missing information. Apparently the poisoned arrow was meant for Mercer, and was not intended to kill but to paralyse the target. Karliah wanted to keep Mercer alive, and to have him pay for his crimes in front of the Guild. Luckily the slowing of the heart beat, meant that the Dragonborn could survive the stabbing, and not bleed to death. So Karliah actually saved the Dragonborn's life.

Karliah then explains what needs to be done next in Hard Answers.

Vielsagendes Schweigen