THE DIRE EARTH is a prequel to the Darwin series (of which I've not yet read) and tells the story of an outbreak across Earth that threatens to end mankind, turning all bar a special few (at this stage a mere handful) into zombie-like beings hellbent on killing the uninfected.
Darwin, Australia, is the only place of refuge by virtue of a mass alien space elevator which seems to generate an invisible barrier around the city sprawl keeping those within the vicinity safe from the mysterious disease corrupting mankind.
While the alien structure is mentioned, there's a whole lot of backstory missing as to how it got to Darwin and where the aliens are who brought it there. Also, there is little by way of rationale behind the structures ability to prevent the disease from entering Darwin. I presume these plot threads are addressed in the series proper (this novella was published in ZERO WORLD as a 'bonus' and appears after the Darwin books) but it would've benefited the novella to at least touch upon these aspects, if only in passing as part of the broader Darwin plot design.
As far as a prequel goes, THE DIRE EARTH is okay. It introduces (what I assume to be) key characters who play a part in the novels and gives them a real three dimensional feel; each feels unique and 'real' with their own motives, strengths, and sense of self.
I've added the Darwin books to my 'watch-list' and hope to check out the first installment soon-ish to see where this is all heading.