Astra has finished her training and is now a full-fledged Sentinel, but things are not going well. She suffers from Post-Traumatic Stress Disorder, and the public revelation of her relationship with Atlas has caused her popularity to nose-dive.
To complicate things, the Teatime Anarchist's intervention has changed the course of events—leaving her with lots of knowledge about the way the future was before the Big One, a complete future-history that is now out of date.
And just when she thinks she's getting a handle on things, unfolding events (a bank-robbery and a horrific murder) show that one of the nastier pieces of the old future isn't so out of date after all; unless she solves a murder before it happens, Blackstone is going to die.