All the Hidden Paths (The Tithenai Chronicles, Book 2) by Foz Meadows

With the plot against them foiled and the city of Qi-Katai in safe hands, newlywed and tentative lovers Velasin and Caethari have just begun to test the waters of their relationship. But the wider political ramifications of their marriage are still playing out across two nations, and all too soon, they're summoned north to Tithena's capital city, Qi-Xihan, to present themselves to its monarch.

With Caethari newly invested as his grandmother's heir and Velasin's old ghosts gnawing at his heels, what little peace they've managed to find is swiftly put to the test. Cae's recent losses have left him racked with grief and guilt, while Vel struggles with the disconnect between instincts that have kept him safe in secrecy and what an open life requires of him now. Pursued by unknown assailants and with Qi-Xihan's court factions jockeying for power, Vel and Cae must use all the skills at their disposal to not only survive, but thrive.

Because there's more than one way to end an alliance, and more than one person who wants to see them fail . . . and they will resort to murder if needed.