Nightwatch over Windscar by K Eason

Set in the universe of Rory Thorne, the second book in this sci-fi series follows unlikely allies who must discover the secrets of ancient ruins.

Iari is good at killing monsters. As a templar in the Aedis, a multi-species religious organization committed to protecting the Confederation, eliminating extra-dimensional horrors is her job. But after she helped stop separatists from sabotaging the entire Confederation, she discovered a new sort of monster: the rogue-arithmancer, political kind.
Promoted and sent north to the tundra of Windscar, Iari leads a team of templars to investigate ancient, subterranean ruins, which local legend claims are haunted, and which have mysterious connections to the dangerous arithmancy used by the wichu separatists. Iari isn't worried about ghosts. She's worried about surviving separatists and a fresh attempt to upend the Confederation.
Included in Iari's team are Char, a decommissioned battle-mecha and...

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