This mission is acquired after completing Priority: Geth Dreadnought. To start the mission, orbit the planet Rannoch and select Geth Comm Hub.
This mission must be completed prior to starting Priority: Rannoch, as it will not be available afterwards. It is quite easy, involving only puzzles and no actual fighting. It also passes you two Intel Terminal upgrades simply for completing it. Although you are asked to select squadmates for this mission, they do not really participate in the mission, they only talk during cut scenes.
After exiting the access point, you are notified of data clusters containing infected code which you need to disrupt to access it. Shoot your way through the first barrier showing up, then before you go any further, search the trail to your left; a small section of the orange tendrils to the left of the trail with orange data fragments floating around the solid code contains Reaper Code Fragments which you can retrieve and give to an asari looking for them. The data tendril cannot be destroyed, nor can the data fragments, however it can be interacted with (like a terminal or data pad) to obtain the code fragments. It is very easy to miss.
Proceed to disrupt the infection of the data clusters which takes the form of a large rounded object. Once you complete the task, the infection enveloping the data disappears and a historical video data will be played. A new path will be revealed which leads to the next data cluster. As before, repeat the disruption process and another video is played after you are done clearing the infection. Finally, proceed to the third data cluster, but just sit back and watch the video since this data cluster is uninfected. Once the video data ends, enter the access point revealed in front of you.
As the scene switches over to reality, a short cutscene shows one of your team members is being contacted by Admiral Raan, notifying that half of the geth fighters in pursuit stopped functioning, most likely due to the actions taken by you.
Back in the virtual world, you are informed that the Reaper code has adapted and can now self-replicate. If you attempt to disrupt the infection in front of you, it will restore itself. Thus, you need to search along the code trail and target its vulnerable point which is just above you. Disrupt the infection to continue.
If Legion was activated in Mass Effect 2, another video data depicts Shepard's first encounter with Legion. This scene will not occur if the Geth VI is present. The access point will be activated after the video ends. You will be shown with another cutscene showing the rest of the geth squadron stopped functioning when Shepard steps into the access point.
As you come out of the access point, head towards to the exit pod across of you. Once Shepard's back to reality, a dozen or so Geth Primes exit their pods as well, surrounding your squad. They do not attack, but volunteer to join you in the fight against the Reapers instead.
- It is possible to walk off the map during the third portion of the mission by stepping off a 1x2 gap, near the data node with the first quarian protester.
- At one point, Shepard asks why the quarians are shown masked in the historical footage, and Legion in turn asks how many quarians had Shepard seen unmasked. If Tali was romanced in Mass Effect 2, Shepard says he only ever saw one, to which Legion replies that Shepard's perception does not match the historical data.
- Upon viewing the hologram of Shepard and Legion's first interaction, it should be noted that Shepard is wearing the Mass Effect 3 Cerberus uniform instead of the one from Mass Effect 2.
- At the end of the mission as their servers are shutting down, if the geth VI is in the play-through, the subtitles will still refer to it as Legion.