Sun-Daughters, Sea-Daughters

Gene-edited human clans have scattered throughout the galaxy, adapting
themselves to environments as severe as the desert and the sea. Atuale,
the daughter of a Sea-Clan lord, sparked a war by choosing her
land-dwelling love and rejecting her place among her people. Now her
husband and his clan are dying of a virulent plague, and Atuale’s sole
hope for finding a cure is to travel off-planet. The one person she can
turn to for help is the black-market mercenary known as the World
Witch—and Atuale’s former lover. Time, politics, bureaucracy, and her
own conflicted desires stand between Atuale and the hope for her adopted
clan.