Captain's Fury (Codex Alera Series #4) by Jim Butcher

In his acclaimed Codex Alera novels, #1 New York Times bestselling author Jim Butcher has created a fascinating world of elemental magic. Now, as enemies become allies, and friends become bitter foes, a danger beyond reckoning looms for all...

After two years of bitter conflict with the hordes of invading Canim warriors, Tavi of Calderon, now Captain of the First Aleran Legion, realizes that a peril far greater than the Canim exists—the mysterious threat that drove the savage Canim to flee their homeland.

Tavi proposes attempting an alliance with the Canim against their common foe, but his warnings go unheeded. For the Senate’s newly-appointed military commander has long desired to wipe out the Canim “scourge,” and their slave allies.

Now, Tavi must find a way to overcome centuries-old animosities if an alliance is to be forged, and he must lead his legion in defiance of the law, against friend and foe—or none will have a chance of survival...