Part 1: Dawn
As we begin the game, look up when prompted and hit the action button to exit the stasis chamber. After a short scene, we’ll have full control of the chief.
Move forward and instead of following the hallway towards the yellow hologram at the end, climb down the stairs and find the computer terminal down here. Interact with it for an achievement.
Found and accessed Chief's record in mission 1
Continue to the room with the yellow hologram and continue through the various rooms until you reach a map room. A red wave of light will wash over the area and the door at the far end from where we entered will open. Continue through the hallways until you get an objective marker on an elevator. Hit the action button and mash the button to open it.
After a short scene, you will be inside hanging off the wall. Push forward to climb up the elevator shaft. When you can climb no further, hit left to jump over. Continue climbing upwards and again jump to the right when you can climb no further. Jump to the right again, climb and then jump back to the left, climb up once more to climb out of the elevator. At the top, press the melee button during the scene.
Following on from this, continue through the open doorway and sneak up on the elite at the top of the stairs and assassinate him (melee in the back for an instant kill). Drop down to the ground floor of the room and kill all of the grunts running around in here. Once the room is clear of hostiles, return to where we killed the elite and hit the switch on the terminal to open the shutters.
Exit the lift and enter the door on the left at the end of the hall. Kill the pair of grunts and elite in here. Turn right and wait for the door to open, in this room are four grunts and an elite, eliminate them and continue along the hall. Drop down the stairs and enter the hallway, again you’ll find an elite accompanied by a group of grunts… you know what to do.
Continue out the back of this room and into the next. Turn a corner to the left to find yet another group of grunts with an elite. Once all of them are dead, the two doors at the back of the room will open, revealing a pair of shield toting jackals. Kill them and continue through the now open door.
Turn left and exit into a large room with a smaller, glass walled room in the center. There are around 10 grunts a handful of jackals and a pair of elites in here to deal with. Once the room is devoid of hostiles, exit through the open door on the opposite side of the room from the entrance. Turn left and in the hallway here wait for the door to open.
This will activate a piece of machinery in front and on the opposite side of the area. Quickly run over to this, after a moment, Cortana will let you know that it needs manual intervention. So interact with the objective marker for a short story scene.
Once the scene has played out, look back towards where we first entered the area and to the right you will the new objective marker continue over here to see a ramp leading up. Climb this and enter the door at the top to find yourself in a semi-circular room. Wait for the door at the far end to open.
Continue through the hall here and run across the next room to the stairs slightly to the left. At the end of this area, turn to the right and enter the door. Wait a moment and the roof will cave in. use the broken catwalk to the left to walk over to the far side of the room and hop through the door. Continue along the hallway until you reach a larger room. Again the roof will cave in. When it does fall down, drop down to the ground floor and enter the door on the far side of the room.
Sprint and jump across the gap and upon reaching the hallway turn right. Follow it all the way to the end to find a door we can approach to complete the mission.
Complete Mission 1 on any difficulty