There are, to date, three books in Graydon Saunders’ Commonweal universe. They are not a trilogy, though they involve overlapping sets of characters in more or less linear timeflow – so it’s a series. The March North, A Succession of Bad Days, and Safely You Deliver are available on Google and Kobo and probably Smashwords as DRM-free ebooks. Minor spoilers for details and word usage follow – not plot.
O’Malley follows up the tight-single-viewpoint The Rook with a multiple viewpoint political/espionage/action fantasy about the secret UK agency in charge of supernatural defense and its negotiations with the Belgian Scientific Brotherhood of Scientists, their traditional enemy. Sorcerors versus mad scientists, basically, with some terrifically funny scenes and a good bit of action.