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. ... Without giving away any spoilers, the reader feels like the cozy universe of Pax Britannia is truly, irreversibly changing.
The inspiration for the cover - the poster for the movie Le Voyage Dans La Lune