An anonymous message suggests sinister motives behind the capture of the salarian ark. Follow the leads to uncover the truth.
Acquisition
After helping Paarchero, the salarian Ark, escape from the kett, Kallo requests to speak to Ryder after receiving an anonymous message.
Walkthrough
Kallo has received an anonymous audio message from someone claiming that that the Paarchero was not captured by chance. There's no more information. If Ryder wants to know more, he'll have to go meet the sender on Havarl
Go to the meeting point on Havarl
The meeting point is in the cave at the south end of the ravine, near where you enter the Mithrava Ascent.
Stop the ambush
As Ryder and party jump over the wall which looks down on the meeting point, a kett shuttle arrives, with an Anointed and several Chosen.
Search the area
Two large cases are in the area. One contains just kett rations, but the second contains a net launcher, restraints, and sedatives; clearly, the kett were planning to take someone alive. Examining the case after scanning it reveals who that someone is: Major Saelen Varn of the STG, now retired, who emerges from the shadows and introduces himself to Ryder. Varn believes that the capture of the Ark wasn't by chance. His best suspect is the biologist Dr. Aden, who is studying the kett, and he needs a Pathfinder to determine the truth of the matter. (Varn didn't go to the salarian Pathfinder with this because he's not sure he can trust the Pathfinder's team not to be part of the conspiracy, but Ryder obviously had nothing to do with what happened to the salarian Ark.)
Varn needs Ryder to examine Dr. Adens equipment and a kett who might be Dr. Aden's handler. Both can be found on Voeld.
Completing this stage gains 29 AVP and +2% viability for Havarl.
The following two objectives can be done in any order
Scan evidence from kett handler on Voeld
The kett handler can be found at a small base in the open on Voeld. Even if the Vault has been activated this will still be a hazard area, so fight your way inside to get warm if you can't dispatch the kett quickly. You'll be fighting several Chosen, a Destined, and an Anointed. The handler himself has armor, unusual for a kett.
Scanning the handler shows that he has a Milky Way transceiver implanted under his skin, for some reason.
Completing this stage gains 29 AVP and +2% viability for Havarl.
Scan Dr. Aden's equipment on Voeld
Dr. Aden's equipment is in the back of the Techiix settlement, which can be easily reached from a forward station if you've ever been there. There are two pieces of equipment. Both can be scanned for 10 
. The mass spectrometer shows signs of chemicals used in the exaltation process, which may be evidence against Aden, but doesn't really prove anything
Completing this stage gains 29 AVP and +2% viability for Voeld.
When both of these steps are completed, Ryder decides to consult the salarian Pathfinder
Speak to Raeka/Hayjer about your findings
The Pathfinder thinks there's probably something to all this, but can't get Ark leadership to do anything either, and therefore suggests that Ryder visit the apartment of Rand Lon, an Ark oficer who woke early. If Lon won't talk, perhaps the scanner will pick up something.
Search Rand Lon's apartment
Lon's apartment is with the other apartments near the docking bay. Lon isn't home and the door is locked, but SAM can hack it. Inside, a terminal has some messages which are either strangely worded or coded. Scanning the personal terminal reveals that data was recently cleaned from it. Scanning the plant in the kitchen reveals a cotton fiber with a neurodepressant chemical stuck to one leaf. Scanning the bed reveals that Lon, or someone else in the room, has tracked back dust from an alien world. Scanning the coffee table reveals a talcum powder spill, and scanning the kitchen counter reveals what Lon had for breakfast; these last two probably won't be very important to the investigation. SAM believes he can determine exactly where the dust came from. (You'll find out later that it's Elaaden) When everything's scanned, your next objective will be to leave the apartment
Leave Rand Lon's apartment
Ryder bumps into Rand Lon at the door to the apartment. The upshot of the conversation is that Lon says Varn is being paranoid, and that Ryder shouldn't bother with the investigation. But there's still the matter of that dust, so..
It's in the far north, and not all that close to shade or a forward station, so watch your life support if Elaaden's environment is still hostile. The navpoint is near a crashed shuttle. Nothing else visible but a lot of sand.
Scan the surface
On the northwest side of the shuttle you'll be able to scan footprints, which indicate that multiple individuals dragged something heavy off to the southwest.
Follow the tracks
Over the ridge you'll see a bunch of scavengers. The trail leads right to them, so obviously, the next phase is...
Defeat the Scavengers
Not much cover here, and you're facing 2 Adhi, an Anarchist, and a bunch of Raiders. Depending on your party and build, your best play might be to charge the camp in the Nomad. You'll also find Saelen Varn here, injured but alive
Help Saelen
A little medi-gel gets Varn on his feet; you learn that Aden's had him shot with a poisoned dart. You also learn that that you've never actually met Varn before. Dr. Aden was impersonating Varn earlier, using a stolen camouflage device. Apparently, Ryder's scanner is powerful enough to wipe data from the communication system Aden's been using, so Ryder's investigation so far has accomplished nothing except covering Aden's tracks.
Varn's convinced that there's a conspiracy here. Even though Aden is guilty, a biologist wouldn't have been able to change the Paarchero's course and hand it over to the kett, so others had to be involved. Fortunately, the dart offers leverage over Aden, since it can provide evidence that Aden's guilty of attempting to murder Varn, at least. This means that Ryder can draw Aden out into a meeting on neutral ground, which turns out to be a set of caves on Kadara.
Speak to the impostor in Kadara's caves
As you enter the marked cave, SAM warns that there's toxic gas present. Entering the cave, you find Fake Varn, but Ryder isn't willing to play along with the charade any further. So Dr. Aden reveals himself, just as the real Varn shows up. Aden reveals that his group, believing that the kett were invincible, decided to pretend to be collaborators in order to infiltrate the kett and destroy them later. (Dialogue here will be a bit different depending on whether you've finished the main quest or not.) Aden claims to have a lot of valuable intel on the kett, and wants to trade that intel for freedom for the conspirators. Ryder can accept the deal, or arrest him. If Ryder accepts, the Kett: Secret Intelligence codex entry becomes available ( you can find it here). Otherwise, Varn arrests Aden, and will search for the other conspirators.
Note: the container next to Fake Varn/Aden will vanish after concluding the mission, so loot it before talking to Aden.
Rewards
1330 XP for completing the mission.
Earlier mission stages grant a total of 87 Andromeda Viability Points and +2% viability for Havarl, Voeld, and Elaaden.
Aftermath
If Ryder accepted Aden's deal, this email comes in:
If Ryder ordered Aden's arrest, this email comes in: