Books in the Dire Earth Cycle series

The automated alien ship came and built us a space elevator - an impervious thread connecting Darwin, Australia to the heavens. We took advantage of the Builder's gift and established orbital colonies along the cord. Then, years later, a plague almost completely obliterated the world's population...

After discovering the first key in the wreckage of a crashed Builder ship, Skyler Luiken and his crew follow the migrating aura towers in search of the four remaining relics. But time is running out...