Citadel: Meeting Garrus

Make your way to Chora's Den. You can walk or use the Citadel Rapid Transit terminal south of the Council Chambers.

Upon entering the area outside Chora's Den, you will be attacked by two Assassins. These enemies have health regeneration and may use abilities like Immunity (indicated by a white health bar) on higher difficulties. Focus fire on one at a time to defeat them quickly.

After defeating the Assassins, enter Chora's Den and proceed to the southwestern end of the bar. You will witness an encounter between Wrex and a krogan bouncer, which updates or starts the mission Citadel: Wrex.

Instead of pursuing Wrex's objective, head to find Harkin.

Talk to Harkin. Exhaust his dialogue options to learn that Garrus is at the Med Clinic and to earn XP. Your dialogue choices here do not affect Paragon or Renegade points.

Head to the Med Clinic, located on the far eastern end of the Upper Wards. You can pass through the market; you may encounter Emily Wong and start the assignment Reporter's Request.

Enter the Med Clinic. You will find yourself in a standoff, and after Garrus intervenes, you will need to defeat several thugs. These thugs are less dangerous than the Assassins; use cover and abilities to defeat them.

After the thugs are defeated, talk to Garrus. Your dialogue choices here do not affect Paragon or Renegade points. You will learn that Fist is working with Saren and that a quarian has information implicating Saren in the attack on Eden Prime.

Garrus will ask to join your squad to help bring down Saren. Accept his request.

The topic of Wrex will come up. You can find him at C-Sec Academy if you wish to recruit him.

To continue the main mission and expose Saren, head to Chora's Den to confront Fist.