In Mass Effect 2, staying one step ahead of the Collectors isn't easy. Fortunately, the Illusive Man has his mysterious finger on the pulse of the galaxy. When word of a planned Collector attack against the colony world of Horizon reaches his ears, he immediately sets Shepard to task on stopping it.

This mission becomes a priority for Commander Shepard after completing recruitment missions for Mordin, Jack, Garrus and Grunt; however, Grunt doesn't need to be released from the tank to activate it. Because it is a priority, Shepard won't be able to do anything else once notified the Illusive Man wishes to speak with them in the comm room. To ensure Shepard is at the highest level possible before embarking on this mission, complete all N7 assignments and tasks from the Citadel, Normandy and Omega, as well as all available DLC missions, before recruiting the last squadmate.

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Mission: Arrival on Horizon

After the Illusive Man's briefing on the mission, there's a cut scene of events on Horizon explaining the GARDIAN laser turrets and their current dysfunction due to a calibration error. To correct this error, the Alliance Military sent one of Shepard's former squadmates, either Kaidan Alenko or Ashley Williams (whichever squadmate survived Virmire), to attend to the situation. During this cutscene, the Collectors attack the colony, dropping swarms of seekers who sting and incapacitate the colonists for collection and transport.

Shepard arrives on Horizon in the middle of the Collector attack, immediately taking cover and sneaking forward to take the enemy by surprise. Continue to advance slowly as more Collectors drop in to join the fight. Once they've been eliminated, comb the area for heavy weapon ammo pickups and hack the datapad on the table for 6000 credits before moving down the pathway into the next area. A group of Collectors are in mid-harvest. Eliminate them and the husks, then head inside the nearby building to pick up a datapad worth 4200 credits. Back outside, scan the dead Collector on the ground for the Heavy Skin Weave upgrade.

Turn the corner, and upon seeing a dead husk, a cutscene initiates wherein Shepard notes that these husks are different from those encountered on Eden Prime. Before detection, head up the stairs and enter the building to bypass the wall safe for 4800 credits and grab the medi-gel from the medical station on the left side wall. Return to the combat area and take cover, then battle the incoming Collectors.

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Once they've been taken down, do not move past the pods where the path narrows, as this will spawn more Collector waves. First, pick up ammo drops, items and equipment that have been left in this area. There will be colonists in stasis, suspended in mid-movement around the buildings. Pick up the med-kit from the left-hand building before advancing up the stairs and into the upper-level buildings, where you can find a computer with 3000 credits and some ammo. Returning to the battlefield, there will be a Collector particle beam on the ground; pick that up and prepare for the next wave of combat.

As the Collectors attack, Harbinger reveals itself for the first time, assuming direct control of Collectors to taunt Shepard and direct the battle. Harbinger-possessed Collectors must be taken down as soon as they are under its control. When all the Collectors have been eliminated, move through the area picking up ammo drops, a power cells crate and a computer worth 3000 credits. Head toward the garage building and bypass the door.

Mission: The Starport

Once inside the garage, speak with the mechanic, Delan. During the conversation, Shepard learns more about the attack and that the GARDIAN lasers are how they need to take the Collectors out. Shepard can gain +2 Paragon by asking who he is, or +2 Renegade for telling him to calm down when first encountered. Further into the conversation, another opportunity for morality arises, with +2 Renegade for calling him a coward or +2 Paragon when telling him to wait there. Before leaving, pick up the medi-gel, platinum and access the wall safe for 6000 credits. Stop at the weapons locker and equip the Collector Particle Beam, as it will come in handy in the upcoming fights.

Related: Mass Effect 2 Guide: How to Recruit the Master Sniper, Archangel

Head toward the starport and bypass the gate. Position squadmates on either side of the gate and attack from cover as long as possible to take out enemies. This area introduces a new type of husk, the Scion, which is much harder to take down than regular husks. Once that area is clear, pick up ammo drops, grab the power cells, use the computer for +3000 credits and scan the dead Collector for the Hyper-Amp research upgrade before heading to the computer.

Enter the starport and head for the computer, taking cover and battling through the husks and scions along the way. Once the first wave is clear, begin hacking the computer to get the GARDIAN lasers online. Between hacks, battle enemies until they've fallen, then pick up the heavy ammo near the doors before heading toward the transmitter. Hack the transmitter, then allow EDI to realign the lasers while fighting off numerous waves of enemies in defense of the tower. Staying on the move is essential in this fight, as lingering in one place too long attracts swarms of husks that quickly become overwhelming.

Just before the fight is finished, another dangerous new enemy appears: the Praetorian. The Praetorian has a particle beam and an attack called Death Choir, both of which are lethal. Wear down its shields and armor, staying in cover and away from its particle beam until it's defeated. With the lasers properly calibrated and online, the Collectors are forced into retreat and Horizon is secure. Delan will emerge, and Shepard can grab some Paragon or Renegade points through conversation with him about doing all they could for the colony. Either Kaidan or Ashley will approach, and there are multiple opportunities in this dialogue for Shepard to earn Paragon or Renegade points, depending on how they respond to their former teammate.

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Mission: Debriefing

The Illusive Man in Mass Effect 3

The former squadmate will question Shepard's loyalty, seeing they are now working with Cerberus, and refuse to join them in their fight against the Collectors. Once this conversation ends, Shepard returns to the Normandy to debrief via holo-conference with the Illusive Man. There are opportunities for up to +4 Paragon and Renegade points here; Paragon for saying they didn't save everyone and no more colonies will get hit, or Renegade by saying they enjoyed the fight and they should go on the defensive. Finish out the dialogue for another +5 morality points, earning Paragon by noting that Shepard's team is strong, and Renegade by telling him not to worry so much.

Perform a final debrief with Jacob to finish out the mission, grabbing +2 more morality points: Paragon by reassuring him their squad can do it and Renegade by telling him not to lose his nerve. Male Shepard can earn an additional +2 morality points by talking to Kelly Chambers about encountering their former love interest on Horizon, gaining Paragon by thanking her at the end of the conversation, or Renegade for saying it was easy.

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