The original book had Byron, Shelley, their crowd of artsy associates, and (protagonist) Michael Crawford. This one, set a couple of decades later, has Christina and Dante Rossetti, their crowd of artsy associates, and (new protagonist) John Crawford. Plus the vampires, of course, in all their shape-shifting, deliriant, disease-or-Muse muddled glory.
Powers is in full form with the creepy grotesquerie. The plot is wall-to-wall sewers, London bird-sellers, quantum interference patterns, surgery, laudanum, and poems buried in coffins. He also manages to work in ghosts and earthquakes (recurring favorite themes that the previous book somehow missed).
I will make complaint only by way of comparison: the story goes by in several fits (from 1845 to 1882), and while each section works well on its own, there isn't as much drive from section to section as there probably should be. Also, the sequel doesn't have nearly as many "holy crap" history or worldbuilding moments as the original. That's inevitable and to even classify it as a complaint is to blush; nonetheless, it was my reaction. Eventually I will re-read the pair in order; perhaps by then I will have internalized enough of the real-life Rossetti, Swinburne, and Trelawny to feel how nicely their fictional histories dovetail. (It's not like I knew anything about Byron or Shelley when I first read Stress.)