Sister Svangerd and the Not Quite Dead - K. J. Parker
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Not even the Church of the Invincible Sun is invincible - and somebody has to do its dirty work. Enter Sister Svangerd and her accompanying priest, both accomplished practitioners. Their mission is simple: to make a meddlesome princess disappear (permanently).
To get to her, they must attend the legendary Ecumenical Council, the once-in-a-century convening of the greatest spiritual minds the world has to offer. But when they arrive, they find instead a den of villainy that would make the most hardened criminal blush. To complicate matters further, it appears that some people long considered dead might not be after all.