Wither by Lauren DeStefano

Rhine and her twin brother Rowan scramble to keep living, even though like all of their generation, they will be dead before they're old. Girls die at 20 and boys die at 25 due to a virus that is so far unexplainable. The First Generations are adults in their 60s, 70s, the first (and only) genetically perfect generation. No one is certain how long they will live, but a number of them, including Rhine & Rowan's parents, have lived long enough to watch their first children die and are now on their next set of children.
At 16, Rhine is taken by Gatherers, people who prowl the streets for girls who will become brood mares to the wealthy, and taken far from her home and imprisoned by Linden and his father Vaughn. Rhine, along with Jenna (18) and Cecily (13), become Linden's wives. His first wife, Rose, the girl he grew up with and loved naturally, has turned 20 and is in the process of dying. 21 year old Linden has married Jenna, Rhine, and Cecily, but pays them little attention while Rose is still alive. Once she dies, he begins to spend time with each of his wives, first at night (each girl has her own bedroom), then during dinner and afternoons. Rhine reminds Linden of Rose, and it is her similarity to Rose (and closeness, the two girls spent time together before Rose died) that draws Linden to her.
Rhine is determined to escape. She does not want to be trapped in the gilded cage of the mansion whose grounds she cannot escape. Her first attempt to run away (during a hurricane) goes badly, and it is her friend Gabriel (one of the house attendants, who is near her age or a couple years older) who saves her from blowing away. Vaughn knows Rhine was trying to run away and warns her of what can happen if she tries again. Part of Rhine's plan is to become Linden's first wife, the wife he brings to parties and out into the world, so she is nice to him without ever really letting him into her past life, she lets him sleep with her in her bed but never consummates their marriage. She finds there is more to Linden than she originally thought, and a friendship grows between them.
Being a sister wife is more fulfilling than she originally thought as well, as she becomes as close as sisters with quiet, withdrawn Jenna and demanding, slightly bratty Cecily. Linden is easily intimidated when his three wives are together and generally lets them have their own way when they are.
Vaughn is a sinister character who had a son live to age 25 then die. Linden's mother died during childbirth and so Vaughn is desperately seeking a cure to the virus to keep his son alive. Rhine thinks Vaughn's desperation leads him to keep Rose's body in the basement laboratory to try different cures.
Wither is the first book in the Chemical Garden trilogy and I am curious to see where the story will go from this book. I really enjoyed getting to know the characters (even Linden) and I don't know what Rhine will do next. She is so intent on getting to her brother Rowan (who may or may not still be at their home in Manhattan) that you want her to find him, but you know even if she escapes from Vaughn, she will still die when she's 20. But you still want her to escape. Wither is definitely a worthwhile read for high school students and older. I look forward to the next book and hope I won't have to wait too long.