A vital depot has gone silent, leaving allied fleets short on desperately needed fuel. Investigate the depot and get it operational again.
The mission becomes available after completing the Priority: Geth Dreadnought mission.
Travel to Cyone of the Silean Nebula. As you enter the facility, walk to the left area to pick up a Rosenkov Materials Chestplate. Then walk further up to pick up a datapad containing the Medical Treatment Plan to complete Citadel: Chemical Treatment mission.Lee Riley and she will explain the situation. A container behind her will be moved to reveal a corridor. Do not attempt to go near the left edge as the area below is filled with toxic gas. On your right, you will come across a Crane Display terminal but before activating it, walk along the same corridor and salvage spare parts worth 4,000 credits.
Activate the crane and a display will appear. The display shows a live video feed which is recording from behind you. You will need to use the 3 buttons to move 2 containers, which are displayed on the left of the screen, to the right.
Once the path is cleared, Riley will then get into position, sending you to go find a way to vent the area. From the Crane Display, follow the path all the way around to your right. There will be a control console to vent the toxic gas. After activating it, head to the area that just opened up. You can find a PDA next to the Fuel Rod Control for 3000 credits, and a medkit in the same area far back by the yellow vehicle.
Come back down the way you came, and either go down the ladder or stairs. Go to the fuel rod control and unlock the fuel rods. Next, different enemies such as Husks and Marauders will come and attack.
After you have cleared the area, you will need to seal the two moderator tanks. (If you need help on where they are, use your objective button depending on what system or console you use.)
Near the reactor controls is another pad with 3,000 credits. Next, restart the reactor. After you so do, the same enemies from before will come attack. Husks will come from the ground, but Marauders will come from above. There are barrier creating devices which can bolster Reaper forces but can just as easily be destroyed to prevent this from happening.
Once your area is clear, Riley will talk to you over comm and say how they are not going to make it. You can choose to help or ask her to keep at it. You will be required to send a squad member if you choose to help.Marauders and a Brute. Once you dispatch the enemies, initiate the final startup on the console. Go straight down to the extraction point.
You have the option to talk to Riley (if she survives) before you leave to go back on the Normandy. Completing this mission gives you 5 reputation, 10,000 credits, and the Advanced Starship Fuel War Asset.