Walkthrough Editbatarian contact, Narl, on the Presidium Commons. Go to Apartment 86. Narl explains to Shepard that he told the Blood Pack he's turning the Commander over to Kreete, a vorcha Blood Pack leader, but Narl also adds that this is a lie.
The real goal is to lure the Blood Pack out since Kreete is planning to betray Aria. Narl needs Shepard to play along and pretend that the Commander is captured. Shepard can either respond positively or negatively to this request, but ends up going along with it regardless.
Then three vorcha arrive, one of whom is Kreete. As they are about to seal the deal, Narl reveals that the deal is between Aria and Gryll, to Kreete's surprise. Gryll, who's next-in-line to assume leadership, confirms the deal and orders the kill on Kreete. Shepard and Narl will then shoot Kreete and the unnamed vorcha present. After the kill, Shepard advises Gryll not to double-cross Aria, to which Gryll agrees, stating he's ambitious, but not crazy.