Nightwatch over Windscar

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 newly-joined templar, and Gaer, ostensible ambassador and talented arithmancer. As they delve into the ruins, they find remnants of long-ago battles, bits of broken armor and mechas—which unexpectedly reanimate and attack. It seems there is still dangerous arithmancy in Windscar—but the source isn't who Iari expected, and they're far worse than the separatists....