Mass Effect 3 Citadel Quest Cerberus Retribution

As you approach or leave the C-Sec outpost on the Presidium, you overhear a pair of humans arguing about something suspicious involving the murderer of their loved ones. Eavesdrop and then interact with them to start the quest. You will stop the couple from participating in an assassination plot. Return to the C-Sec outpost to speak with Captain Sommers, the man who organized the plot. Deal with Sommers how ever you'd like to.