Ghost Exile book 4. Serious spoilers ahead for the earlier books.
Caina is searching for an assassin who lived a century and a half ago. She gets some clues that send her to the gladiatorial arena. Where, she discovers, to her surprise, that Kylon is fighting as the Exile, she having not had the slightest clue that he was not still in New Kyre with his wife.
It involves why he's there, a fire elemental attacker, Nerina doing some catapult calculations, what Caina must do to learn a secret, the discovery that someone else is a century and a half old and has a grudge against the assassin (who returns it), a prediction involving silver fire, and more