Priority: Tuchanka

Acquisition
The mission is acquired automatically after completing Priority: Sur'Kesh.

Preparation
Immediately after completing this mission, Priority: The Citadel II becomes available, which makes it impossible to visit the Citadel and causes a number of side quests to be lost forever. As such, completionist players should be sure to complete the following side quests before attempting this mission:
 * Benning: Evidence
 * Citadel: Alien Medi-Gel Formula
 * Citadel: Barla Von
 * Citadel: Biotic Amp Interfaces
 * Citadel: Hanar Diplomat
 * Citadel: Improved Power Grid
 * Any interactions with Kelly Chambers. These are only available if certain events were completed in Mass Effect 2, so she might not be present at all; but if she is, you'd better talk to her now. If you told her to "change identity", she will not be available now regardless.
 * Conversing with Matriach Aethyta in the Apollo's Cafe.

Walkthrough
It is advisable to complete any and all business on the Citadel before commencing this mission. Most quests found on the Citadel end immediately upon travelling to the Citadel after the conclusion of this mission.

To complete the treaty between the krogan and the turians, Urdnot Wrex (or Urdnot Wreav, if Wrex did not survive) insists that the genophage must be cured. To do this, the cure to the genophage must be dispersed at the top of the Shroud, a tower installed by the salarians to clean the atmosphere of Tuchanka - and covertly used to disperse the initial genophage virus.

The Convoy and Catacombs
The mission starts off with Shepard heading towards the Shroud in a convoy with Wrex (if he survived the events of Mass Effect), Eve, Mordin, Wreav, and some krogan warriors. The reapers have anticipated an attempt to cure the genophage; to counter this, a Reaper Destroyer has been deployed near the Shroud. To destroy it, the krogan plan to attack from the ground while Turian fighters deploy for air support.

At the first stop you can pick up a shotgun upgrade, 2 pistol upgrades, the Deathmask(armor helmet), the Graal Spike Thrower and 2 medkits.

However, the air support arrives too early - a Turian fighter jet is shot down and hits the bridge in front of Shepard's vehicle, forcing Shepard to find an alternate path forward to the Shroud.

The only path left is through the Catacombs, an ancient Krogan burial site which has been in disuse for millennia. Shepard discovers that the area around the shroud is home to "Kalros, the mother of all Thresher maws."

Ruins
Shepard exits the Catacombs into above-ground ruins, and is surprised to find some plant life - evidence that even with most of Tuchanka ground into rubble and dust, life can still exist there. Fully exploring the ruins for murals painted on the walls will also yield 26,000 credits worth of priceless krogan artwork. Toward the end of this area (when you get to the memorial) there is an SMG upgrade and an assault rifle upgrade; the former is near where a Marauder spawns and the latter is by another depiction of Kalros.

As Shepard progresses, resistance is encountered in the form of Reaper ground troops. At the same time, the Convoy is attacked by Kalros - the Mother of all Thresher Maws. One truck is destroyed, and Urdnot Wreav dies if he has not replaced Wrex.

Shepard and the remnants of the Convoy reunite to form a plan for dealing with the Reaper and reaching the Shroud.

The Maw Hammers
Shepard agrees on activating the ancient Maw Hammers to attract Kalros to the area, and hopefully goad it into attacking the Reaper. Shepard heads out activate the Maw Hammers, and Mordin (or, if he did not survive the events of the previous game, Padok Wiks) starts finalizing his work on the cure to the Genophage.

After the first skirmish, you will go up a set of stairs. At the top, on your left is a pistol.

To reach the controls to the two maw hammers, Shepard has to fight through a gauntlet of Brutes, while avoiding getting crushed by the Reaper. Kiting the Brutes is an option, particularly if armor-damaging skills are available.

Alternatively, simply dash through the battlefield, tagging the Maw Hammers via superior speed. At this point, the Reaper's legs are the biggest threat: one hit will knock off your shields and at least one lifebar segment; if the Reaper lands a second hit before your shields regenerate, it's an instant kill. Thankfully, the Reaper's leg-stabs seem to be location-based events: as you approach certain specific spots on the map, a leg comes down. Many of the stabs are focused on the two catwalks leading to the maw hammers. As such, the safest approach is to run across the arena and then walk down the catwalks. Also, you can see where the Reaper is going to hit roughly two seconds before it happens by looking for the giant shadow cast by its leg. That's enough time to dash to the side and avoid running into the thing.

When both hammers have been activated, they successfully attract Kalros, which destroys the Reaper.

The Shroud
With all opposition from the Reapers destroyed, Shepard and the convoy approach the Shroud. However, the Shroud sustained damage in the fight against the Reaper - it is falling to pieces as Shepard and Mordin approach. Mordin must travel to the top of the tower to counter the STG sabotage which was installed years ago by the salarians. Mordin is also tasked with overseeing Eve's wellbeing; if he lacks Maelon's data, she will die whilst Shepard is tangling with the Reaper.

At this point, Shepard may either let Mordin go or stop him, to sabotage the cure per the Dalatrass's request. There are multiple outcomes to this conversation.
 * Shepard may let Mordin go. If so, Mordin sacrifices his life repairing the STG sabotage and the genophage cure is successfully released.
 * Shepard may attempt to stop Mordin using normal conversation. If so, Mordin insists on continuing, and Shepard is forced to use a Renegade interrupt to gun him down.  (This opportunity is available even if Shepard already confessed the dalatrass's proposed deception, though it is logical to assume that Mordin's dialogue might change to reflect his forewarning.)
 * Shepard may also have Charm and Intimidate options available. If so, Mordin agrees to delay the genophage cure until after the Reaper threat has passed, and to become a War Asset at the Crucible project in the meantime.  It has been claimed elsewhere that the Reputation checks are only available if Wreav leads Clan Urdnot and Eve has died.

It is unknown at this time if having Padok Wiks present instead of Mordin also opens or limits outcomes. Any research is likely to be time-consuming, since the interaction of Wrex/Wreav, Mordin/Padok and kept data/deleted data results in eight separate outcomes, multiplying to at least 16 once the above choices are factored in.

Aftermath
This mission results in the following outcomes:
 * The turians enlist as War Assets.
 * Whether or not you actually cured the genophage, the krogan enlist as War Assets. However, they may be diminished in strength if Eve died.  Furthermore, if you did not cure the genophage, Wrex will eventually find out, and emerge from the elevator to confront you during Priority: The Citadel III, leading to Wrex's death and a further diminishing of krogan value.
 * If Wreav is the Urdnot leader, he never discovers the deception. However, he isn't able to do a very good job of holding the krogan together, leading to diminished krogan value as War Assets and as defenders of Palaven, at least according to Primarch Victus during Priority: Earth.
 * If you cured the genophage, you will receive no salarian assets at this time, leaving the STG force you gained from Major Kirrahe (if you did so) as their race's only representatives. However, the events of Priority: The Citadel II--the very next mission--will give you a chance to win their respect.  If you were able to spare Mordin, he will enlist as well.

Given that the Salarian Fleets are ~150 points, and Clan Urdnot + Wrex is ~325 points, a Renegade-minded player should be aware that not curing the genophage will actually weaken your force. However, this has not yet been confirmed for all cases of failing to cure the genophage, but merely all cases of killing Mordin plus all conversation options during Priority: The Citadel III.