Blood Red Road (book 1 of the Dustlands series) / by Moira Young -- In a distant future, eighteen-year-old Lugh is kidnapped, and while his twin sister Saba and nine-year-old Emmi are trailing him across bleak Sandsea they are captured, too, and taken to brutal Hopetown, where Saba is forced to be a cage fighter until new friends help plan an escape.
“Ever heard of the rule of three? he shouts as we run. No! If you save somebody's life three times, their life belongs to you. You saved my life today, that makes once. Save it twice more an I'm all yers.” Moira Young, Blood Red Road (Dustlands, #1)