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Depot Sigma-23

The data you found at Listening Post Theta indicates that a supply ship came from Depot Sigma-23 in the Gorgon system just before the attacks on Listening Posts Alpha and Theta. That supply depot is likely where this rachni infestation originated.


This assignment is acquired from a terminal on Altahe or from Lt. Durand on Nepmos. However, both prerequisite assignments must be completed to get the facility's location.

If Listening Post Theta is done first instead of Listening Post Alpha, this assignment's journal entry may be obtained just before exiting the station. In this case it may be necessary to go back to Listening Post Theta and interact with the terminal again for the Gorgon system to be accessible.


This assignment involves fighting a lot of rachni in a cluttered freighter environment, so powers such as Neural Shock, Throw and Lift are quite useful. Shields on the other hand will be useless, as will talents intended to overheat shields and weapons. Damage prevention and toxic resistance armor mods will come in handy, as will Shredder, Hammerhead, and Sledgehammer rounds.


After learning that the rachni appeared after an automated supply delivery, travel to the Gorgon system in the Argos Rho cluster and board the Unidentified Space Facility. The entryway is clear of enemies, of anything for that matter. The rachni that are aboard are waiting for you and your squad, so it would be rude to keep them waiting.

Remember this layout well - this WILL save your life later. For reference, you came in from the door with the green knob, from the left.

The main hold of the ship contains seven Rachni Workers, and one solitary Rachni Soldier. Once you enter the hold take a left because that is where the soldier is. Take it out first because it is the greatest threat, then turn around to combat the workers. Once the workers are down turn around and hack the two weapons lockers (one requiring Easy Decryption, the other requiring Hard Decryption) in the area where the soldier was. Then proceed to the forward section of the ship.

On your way to the forward section of the ship be on the lookout for more containers on the way. In this order from the entrance door to the forward section: a secure crate requiring Average Decryption; be careful because this is easy to miss. Then a wetware kit is hidden in an alcove. A technician kit, this is another easy one to miss. Just before the door to the forward section is another locked crate, which requires Easy Decryption. Before going through the door, move around the corner and pick up an upgrade kit.

Entering the forward section of the ship head to the right first because this room contains containers that you will miss when you activate the charges. The room contains a medical station (Easy Decryption required), a crate, 2 storage lockers (one requiring Easy Decryption, the other requiring Average Decryption), and an upgrade kit. The cockpit contains nothing, so it is worth passing up. Try to remember this route because you will be making your way back, and in a hurry.

In the left module, you'll find a terminal with data logs by Major Elena Flores. Listen to the logs to get an idea of what happened here:

  • The first log entry describes that the station is operational. The log says that they will be adding the barracks and stocking munitions. Flores says that they will have room for two reinforced platoons of Cerberus Commandos.
  • The second entry describes the package arriving and how these ones are supposed to be different. Something about developing in proximity to the master control unit. Flores documents a plan to 'test' the rachni by unleashing them on some local pirates.
  • The third entry describes that the rachni have escaped, accessing the freighters and setting them to random destinations. It goes on to tell how the Cerberus personnel "treated them like animals. We should have treated them like POWs." Flores tells someone called the General, to "screw the rachni" and destroy the station.

Now that is what you will do. Next to the terminal are some demo charges. Be warned that once you access it you will have only 01:10 or 70 seconds to get back to the Normandy. Before you set off the charges make sure you have all the goodies that are spread all over the station. When you are ready set the charges, now all you have to do is RUN.

More rachni will spawn the second you arm the scram charges and attempt to block your access back to the Normandy. Five Rachni Workers and a Rachni Soldier will be waiting outside the door from the forward section to the main hold to block access. Send in your squadmates first then follow. Take out the rachni fast then double-time it to the Normandy. Once you reach the Normandy leave because every second that you wait at the airlock is another second off the clock. THE CLOCK DOES NOT STOP. Once you leave you will complete the assignment.

Note: The cargo hold layout is exactly the same as the layout of the MSV Cornucopia in the assignment UNC: Derelict Freighter.



  • Even if you investigate this mission after completing other missions relating to Cerberus, your party may still ask about Cerberus as if they've never heard the name before.
  • In the Mass Effect 2 assignment N7: Lost Operative, Shepard is tasked with recovering data which could "conclusively prove Cerberus' involvement in rachni experiments" from an Eclipse base.
  • Joker references Cerberus' failed experiments on the rachni as one of several examples of the organization's incompetence at the party in the Mass Effect 3: Citadel DLC.
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