Priority: Horizon | Mass Effect 3 Wiki

Priority: Horizon Full Walkthrough

Getting Started

This mission is automatically acquired upon the conclusion of Priority: Thessia.

This mission will involve a plot concerning Miranda Lawson and her family. If Miranda survived the events of Mass Effect 2, she will be pursuing her sister Oriana Lawson who has disappeared. Miranda suspects her father Henry Lawson is involved. If Miranda did not survive, Oriana will have sent you an e-mail prior to this mission in which she states she has run into trouble in Sanctuary and will take the place of Miranda for the numerous video logs found in the facility. The conclusion of this plot will be influenced by your actions during the three times Miranda invites you to meet throughout the game. This guide assumes Miranda survived and is present in the playthrough.

You will be faced with a mix of Cerberus and Reaper forces making it imperative that you bring along squadmates and Powers that can deal with the heavy shields and armor possessed by these units. You can also focus on shield-disrupting Powers and bring along weapons with armor-penetrating properties or mods.

When ready, chart a course for Horizon in the Iera system.

Walkthrough

The mission opens to a cutscene with a broadcast from Oriana, warning recipients to stay away from Sanctuary. Once you land, approach the building ahead of you behind all the rubble. A Cerberus shuttle crashes just ahead after being attacked by a Harvester which immediately flies away.  A couple of Phantoms and a Nemesis emerge from the crashed shuttle. Defeat the enemies and then move forward. There are some parts you can salvage on the right for 1,500 Credits. Bypass the door controls at the very end and pick up the Med Kit to the right of the door on the inside.

Your squad notices several Cerberus shuttles emerging from a tower visible from openings in the ceiling, with Shepard remarking that that's where you're headed. There are several audio logs and datapads you can examine in this area if you want some backstory on what happened. Otherwise proceed down the stairs. Check the side of the crashed shuttle for a couple of audio logs and then proceed down the path right of the stairs. You will come across some dead troops from both Cerberus and Reaper forces and some live Assault Troopers just around the corner. Once you engage them, more will appear from the back of the hall. Take all the troopers out and then pick up the Pistol Scope from a corpse around the central desk. Go past the desk and turn left into a dark corridor and follow it around the corner where you can salvage some equipment worth 1,500 on the right wall.  Inspecting the console will reveal a message from either Miranda or Oriana stating that Sanctuary is not a refugee camp but a Cerberus facility run by their father. The sisters urge listeners to turn back saying that there is no help to be found here. Proceed towards the outer area on the right where you will see a large pool of sorts. Activate the security panel just before it which drains the water from the pool, revealing a backdoor into the facility.

Climb down the ladder and proceed towards the door on the opposite end of the pool. Head inside and proceed past a second door then look to the right wall for some equipment worth 1,500 Credits. Pick up the Rosenkov Materials Shoulder Guard left of the next door. The next room is a control center of sorts but the room is powered down. Activate the console in the center to bring the power back online. The monitors up above reveal footage of Cerberus agents rounding up refugees and turning them into Husks. Shepard approaches another console, turns the power on, illuminating a chamber behind the glass where several refugees-turned-husks scramble and scale up the walls around the control room. Head for the exit on the other side.

There is a row of terminals in the next room where you can examine a PDA. Walk down the steps and into the kiosk at the back to find another console which contains a video log of Miranda shutting down power to the processing plant to lock the Husks inside. Kai Leng also appears in the footage prompting the squad to move and find Miranda. Move down into the lower, central area of the room and head through the door. There are Husks waiting behind it. Clear them out and proceed down the steps. There is another row of terminals here with a couple of audio logs concerning Henry Lawson. Head through the opening behind the terminals leading to a long corridor with several Marauders, Ravagers and a Banshee. There is also a Barrier Engine way in the back. After the battle, proceed down the corridor and turn left. There is a Med Kit and two more audio logs in this room. Proceed towards the door past the glass window with a Banshee behind it. It cannot attack or get to you.

In the next room is another console with a recorded message from Miranda announcing that she will attempt to disable the comms scrambler in the tower. There's some research data you can salvage for 1,500 at the end of this side of the room, as well as a PDA you can examine on the desk nearby. Head up the steps to the left of the entrance and enter the lab area through either one of the two doors. There is a large group of Reaper forces here supported by several Barrier Engines, take these out first and then defeat the infantry. When the battle is over, search the right side for an M-12 Locust SMG and a Shotgun Blade Attachment. The left side of the lab houses several more audio logs. At the end of this side of the room is yet another console with a message from Miranda with video evidence confirming that her father is working for the Illusive Man. The evidence suggests Henry had come up with a method of controlling the converted Husks. Another clip shows security footage of Kai Leng catching up to Miranda as Shepard lowers the access ladder.

Climb up the ladder and proceed towards another fight with Reaper forces. Just as before, destroy the Barrier Engines first. Once the enemies are dead, head down the hallway into the next room. Pick up the Med Kit to the right of the door and salvage the research logs on the left for 3,000 Credits. Play the audio logs here if you like and then proceed towards where your squadmate is calling for you on the right. Jump the gap onto the horizontal lift platform and then shoot the hatch off the power box on the right in the center. Activate the controls and the lift will bring you across the large area. Jump off towards the door once the lift stops and begin the final battle sequence of the mission. You will be faced with two Brutes and then a Brute and Banshee combo. These should be nothing new. Maintain your distance as always and use your Powers liberally. Once you're done, head for the end of this large hallway and go around the row of terminals to salvage the research data for 4,500 Credits. Just before the stairs, there is a holographic control unit for the pods in the left side of the hallway. Inspect the control unit and choose the manual override option then head for the first pod left of where you entered for an M-99 Saber Assault Rifle. Now go back to the end of the hallway and open the door on the right which leads to the tower elevator. 

When you reach the upper floor and go through the doors, a cutscene begins with an important confrontation between Henry and one or both of the Lawson sisters. Henry will be holding Oriana hostage and if Miranda is present, she'll be on the floor reeling from her injuries from her fight with Kai Leng. This scene can play out in multiple ways:

• A Reputation check will determine whether or not you can Charm or Intimidate Henry into releasing Oriana.
  • Passing the check without Miranda present will give you a Renegade option to gun him down.
  • Passing the check with Miranda present will cause her to throw him with biotics through the glass and to his death.
• Not having enough Reputation to take the Charm/Intimidate route will leave you with only the "I just want Oriana" option and the first of two Renegade Interrupts:
  • Taking the first Interrupt will cause you to shoot Oriana in the leg, distracting Henry.
    • If Miranda is present, she will kill her father.
    • If Miranda is not present, you will get a second Renegade Interrupt chance to kill Henry. Ignoring this Interrupt will have Shepard release Henry, asking him to run away.
  • Not taking the first Interrupt will cause one of the following:
    • If Miranda is present, she and Henry will kill each other while Oriana lives.
    • If Miranda is not present, Oriana will thrust herself backwards, propelling both herself and her father through the cracked windows to their deaths.

In the aftermath of the above, the game will determine whether or not Miranda survives her wounds from the fight with Kai Leng by performing a check on your past actions, similar to Priority: The Citadel II and Priority: Rannoch. There are two conditions to meet, or three if you romanced Miranda:

1. Either import a Mass Effect 2 save where you've completed her Loyalty Mission or warn her about Kai Leng during your second meeting after Priority: The Citadel II. Warning her is done by reading the dossier on Kai Leng given by Admiral Hackett before you meet her for the second time. Note that warning her is your only option if you had not imported a save.
2. Allow Miranda to access Alliance Resources at the apartment during your third meeting. Note that not meeting her at all for the third time will also lead to her death during this scene.
3. If you've romanced Miranda and then break off the relationship in Mass Effect 3, she will die at the end of this scene. This will supersede all of the above.

Conclusion

One of your squadmates will be able to salvage some data from the tower which should lead you to the Illusive Man. If Miranda is present, she will inform you that she had placed a tracker on Kai Leng during their fight that should lead you straight to him. The mission Priority: Cerberus Headquarters then becomes available.

You will gain the Alliance Sixth Fleet as a War Asset. If Miranda survives the entire ordeal, she will also join as a War Asset.

Note that starting Priority: Cerberus Headquarters is the point of no return for most activities. If you have some Side Missions or interactions left that you'd like to complete, now is the time to do them as they will all close as soon as you begin the next mission.

Trivia & Notes

• Trivia and notes go here