The Grissom Academy: Investigation, which turns later in Grissom Academy: Emergency Evacuation, is a Mass Effect 3 side mission that must be completed after Priority: Palaven or Priority: SurKesh.
Make sure that this mission is finished before the first main mission of the second act.
When to start
After Priority: Palaven or Priority: SurKesh but before Act 2 Priority: The Citadel.
Grissom Academy needs to be evacuated before the Reapers destroy it, but the ship coming to evacuate the academy faked its signal. Investigate Grissom Academy and rescue the students if necessary.
Kahlee Sanders, Biotic Company or the 103rd Marine Division War Assets
To start the mission, open the Galaxy Map and find Petra Nebula. Travel to the system and then go to Grissom Academy. Land, select your crew and weapons, then watch the cutscene, featuring Kahlee Sanders.
When the mission starts, your objective is to reach Sanders. Kill the Assault Troopers standing between you and her, and then speak to Sanders. At this point there is only one possible route to follow.
The first point of interest is a large hall where a student (Reiley Bellarmine) protects himself from Cerberus with a force-field. On the right side of the room is a Datapad on the red sofa.
Turn around and check the adjacent room, using the door next to the one you have used to get inside. On the stairs is the Assault Rifle Stability Damper.
Enter the classroom near Reiley, through the broken window and check the desks for the Tactical Analysis Review, and the SMG Heat Sink.
When you reach the second classroom, first investigate the hall to the left, for the M-22 Eviscerator, and then go through the hall on the other side. Talk to Seanne Bellarmine, then near her, look for the Mnemonic Visor. On the central sofa is the M-96 Mattock. Get it, then head towards the next door.
When you enter the Orion Hall, you will see some students fighting Cerberus. After the cutscene, kill the smaller troops first, and the Atlas mech after. Talk to Ensign Prangley, and to Ensign Rodriguez.
On the bottom floor check the corners for a Med Kit and a Data Log near the laptop you have to use to deactivate the Cerberus Camera Control.
Now, go upstairs and in the central room, get the Datapad, near the window, then the Assault Rifle Precision Scope near the monitors next to the panel you have to use to override the door. Go down and force the door below the central room.
When you enter the next area, sabotage the turrets, take out the Troopers and the Engineers, and then destroy the Atlas mech. The exit is on the ground floor.
When you enter the passage you will find a Med Kit to the right (on some crates), and a computer to the left (on a bench). Continue to push forward towards the objective until you meet Octavia.
After you talk to her, go right and in the next passage you will find the Biotic Amp Schematics, on a red terminal to the right. Take them so you can complete the Biotic Amp Interfaces Citadel Mission.
Proceed through the next door, and to the left you will find the Serrice Council Chestplate. After you open the next door, take out the Engineer with a head shot.
Near the Atlas mech, to the left, grab the Data Log, and the Med Kit on the bench (to the right). Enter the robot, then go through the tunnel and unleash hell on the Cerberus. Make sure you protect the students.
When the area is cleared, exit the robot check the right side of the hall, while facing the tunnel you used to get inside. On a bench is the SMG Magazine Upgrade.
Get it, and then exit through the marked gate to complete the mission.
New achievement/trophy unlocked: Liberator.
Next side mission is Benning: Evidence.