Main storyline so unmissable. CONTAINS SPOILERS. (Detailed more so than quick version)
- Go to Lt. Davis
- Remove Power Core
- Install Power Core
- Go to center of town
- Cycle the ignition primers
- Find Roland and pick up Eridium nuggets
- Go back to center of town and give to Firehawk/Lilith
- Head toward the Fridge
- Fight your way to the door
Alright, where to begin, you got screwed, lets put it that way. The power core you put in at first ran out of juice so you had to put a new one in that had a virus or something and shut down the shields protecting Sanctuary. So you guys have to get the city flying again which means you have to go to center of town and prime those cells that you put in earlier. Then Roland has some debris fall on him and you need to get the Eridium to Lilith, so go into the building and grab all 5 of them and run out again and give them to Lilith.
After that its a cutscene of them getting attacked and trying to lift off. Eventually they do and you get left behind (of course -.-) so you have to find them, leave Sanctuary and go to the Fridge, have to fight through some rats first but when you get to the door Angel will help you out and after push the button and bam, achievement unlocked. Or, its around that area.