This is the third book in the Silo trilogy, following 'Wool' and then 'Shift'. In many ways though, it is more of a direct sequel to Wool, as Shift is -mostly anyway - a prequel. However don't try reading Wool and then Dust, there are several chapters of Shift that move the story along.
*spoilers for the first two books*
Dust starts off after Juliette has returned to her Silo, the only person ever to come back alive after being sent out to Clean. She comes back with stories of other Silos, and has a crazy plan to dig to the (almost empty) neighbouring silo. She has been elected Mayor, but not many people trust in her. Meanwhile, in Silo One Donald continues impersonating Thurman while trying to help Juliette, and also trying to keep his newly awakened sister a secret.
To me, this is the weakest of the three books in the trilogy. Book One was extremely novel, an introduction to a fascinating world. Book Two explored how the world of the silos came about and is really gripping stuff. Book Three though was a bit flat, there were no big surprises or new problems to overcome. That said, the ending is good, and fitting of the overall series as a hole. I'd give it 7/10.