Shiala is an asari commando, a powerful biotic and former follower of Matriarch Benezia. Commander Shepard's team encounters her on Feros.
Background[]
Shiala was an acolyte of Matriarch Benezia for nearly two centuries, respecting her wisdom and biotic ability. Along with many of Benezia's followers, Shiala accompanied the matriarch aboard Sovereign as Benezia tried to guide Saren Arterius down a gentler path. When Benezia failed and became indoctrinated, Shiala also became one of Saren's thralls.
Shiala willingly served Saren and accompanied him to Feros, where Saren encountered the Thorian and discovered that the ancient alien plant had the Prothean Cipher he needed to understand the vision from Eden Prime. He managed to convince the Thorian to accept a trade. Shiala was 'sacrificed' to the Thorian and absorbed by it, sharing a single consciousness. She then used her biotics to gain the Cipher, which she transferred to Saren's mind. Once he had what he needed, Saren abandoned Shiala to the Thorian and ordered the geth to destroy it, hoping to prevent Shepard from gaining the Cipher.
Mass Effect[]
When Shepard's team arrives at the Thorian's lair, the creature is somehow able to create clones of Shiala which serve to communicate with Shepard. These clones are also biotics who attack Shepard's squad as they try to wipe out the Thorian.
After the Thorian's destruction, Shiala is freed and is fully herself again. She tells Shepard of Saren's actions and how Benezia became a slave to his cause, and explains about the Cipher. Knowing the vision is the key to finding the Conduit, Shiala touches Shepard's mind and directly transfers the Cipher. She assures Shepard they have been given a great gift, and that comprehending the Cipher will take some time.
Shepard then has to decide Shiala's fate: allow her to live, or kill her. In the former, Shiala resolves to stay and help Zhu's Hope. In the latter, Shepard determines that Shiala "switches sides too often" and thus decides to execute her; Shiala will accept her fate and kneel, offering no resistance as the Spectre shoots her in the back of the head.
If Shiala is spared, she can be found outside the Borealis next to the former entrance to the Thorian's lair on subsequent visits to Zhu's Hope. If the colony survived, she pledges to do what she can to assist the colonists, having been ashamed of the damage done to their lives. Alternatively, if too many colonists died she vows to stay and help until everyone else has left.
Shiala is the only individual who has managed to overcome Sovereign's indoctrination without resorting to suicide. This is likely because she was linked directly to the ancient Thorian and 'indoctrinated' by the plant being in turn. After the Thorian died, her mind is her own again.
Mass Effect 2[]
If Shepard allowed Shiala to live after killing the Thorian, she can be found on Illium two years later, investigating a medical contract made with the colonists of Zhu's Hope. Shepard can offer to negotiate with the company on Shiala's behalf. In the months after her exposure to the Thorian, Shiala's skin pigmentation changed to green — similar to her clones — and her biotic abilities became unstable. She also mentions disconcerting dreams of her time with the Thorian.
If Shepard helps her, Shiala also professes an interest beyond mere friendship, saying: "Maybe sometime, when I'm not organizing the colony and you're not... doing whatever you do." She then smiles and strokes Shepard's arm before leaving.
However, if Shepard allowed the Feros colony to die (but let Shiala live after freeing her from the Thorian), then her dialogue and interactions with Shepard will change. She will say instead that she is a commando and doesn't know how to help people, but she will try. She will also not flirt with Shepard once they help her.
Mass Effect 3[]
If Shiala and the Feros colony survived, Shepard will receive an e-mail detailing how the colonists on Feros are fighting the Reapers. Due to the Thorian spores, colonists are given an uncanny ability to sense one another, allowing them to think and act as one in battle. The long-term consequences of this connection are unknown, but helpful for the time being.
Shiala also mentions that she feels as though she is still indoctrinated, as she can feel the Reapers' influence in her mind. However, she says that this is overridden by her connections to the other colonists. She and the colonists contribute to the war effort.