Ship of Smoke and Steel (The Wells of Sorcery Trilogy)

When Isoka's magic is discovered by the government, she's arrested and brought to the Emperor's spymaster, who sends her on an impossible mission: steal Soliton, a legendary ghost ship-a ship from which no one has ever returned. If she fails, her sister's life is forfeit. On board Soliton, nothing is as simple as it seems. Isoka tries to get close to the ship's mysterious captain, but to do it she must become part of the brutal crew and join their endless battles against twisted creatures. She doesn't expect to have to contend with feelings for a charismatic fighter who shares her combat magic, or for a fearless princess who wields an even darker power.