Angel with the Sword — C.J. Cherryh

MEROVINGEN
C.J. Cherryh's fantastic city of canals, where the wealthy and powerful dwell in the highest towers, and the boaters, beggars, spies, and thieves lurk on the highly polluted interlacing waterways below....

MEROVINGEN
where gutsy young canaler Altair Jones earns her livelihood on the danger-filled byways of the canals and in the dark "lower city," always staying just the right side of the law and keeping out of trouble until the night she rescues a high-born stranger from drowning. Then, suddenly, Altair is catapulted into the world of upper-level politics, where games of power are played for keeps, and where a canaler must use all her wit and skill just to survive....