Dark Side is the latest, and certainly the most spectacular, of Jonathan Green's Ulysses Quicksilver series.
Quicksilver, in case you've missed the previous few books in the series, is the silver-tongued gentleman-adventurer whose plan is always to "make it up as he goes along". In Dark Side, this takes him to strange new places - in both geographical and narrative terms...
Perhaps the biggest journey is the actual structure of Dark Side, which goes into uncharted territory for the series. Whereas the previous books were essentially one-offs (although one-offs that rewarded loyal readers), Dark Side builds out of the existing Pax Britannia mythos. Although reading the short story "Vanishing Point" isn't absolutely necessary to understanding Dark Side, it certainly gives you a running start. And, on the other end of the book, Dark Side is the first in the series to actually end with a proper, "ack!-when-is-the-next-book-out?!" cliffhanger.
Dark Side is the biggest book in the series in all respects. By bringing in characters and conflicts from earlier books (some for the last time), Green elevates this from a snappy, pocket-sized adventure into the start of something properly epic. Even bringing Emilia back as the object of flirtation helps make this book more serious and less ephemeral than those that came before it. Without giving away any spoilers, the reader feels like the cozy universe of Pax Britannia is truly, irreversibly changing.