Angel Mage, by Garth Nix

The Archangel Palleniel of Ystara has turned against his people, inflicting a plague that either turns their blood to ash or transforms them into savage, cannibalistic beastlings. Ystara is now a wasteland, its refugees the underclass in neighbouring Sarance because touching them with angelic magic reignites the plague. More than a century later Liliath, the maid of Ellanda, wakes from a very long sleep to lead the refugee Refusers back to Ystara. But first she must find four young people who carry the spark of Palleniel and are essential to her quest. Nix has created an alternative version of 17th century France, where the most powerful are mages who can summon the strongest angels to do their bidding, but pay a terrible price for it; the more and stronger they summon, the faster they age. Liliath is the only exception, as she can summon and even absorb angels without ageing. Unusually for Nix, this book is a slog. It takes a very long time to set the scene, with unnecessarily tedious details of city layouts, buildings and costumes, before the four young heroes are finally introduced. Their stories and characters are as interesting and compelling as those in his previous books, so it’s a pity the story doesn’t start with them, instead of lingering over the details of the unpleasant Liliath. It takes almost 500 pages to get to the rather rushed conclusion in which she meets her fate, but judicious editing would have cut it by a fifth and made it a much more enjoyable journey.