The Wounded Hawk The Crucible Trilogy #2 Sara Douglass 2001
The plague has passed and for a while it seems evil has been defeated. Europe recovers, prosperity returns, trade resumes, and people slowly recover from the effects of the plague.
Then, just as the Church relaxes its guard, war spreads across Europe. Widespread heresies challenge the authority of the Church. Revolts and rebellions threaten to topple the established monarchies and overturn the social order of Europe.
And then the plague returns, worse than ever. Neville eventually discovers the cause. The minions of the Devil have been scattered throughout European society during the confusion of the Black Death.
His task is to discover the identities of these shapeshifters so that the Church can move against them, but it is a dangerous task. They are master shapeshifters so he can never be certain of who he should trust.