A Million Shades of Grey by Cynthia Kadohata
Ever since Tin can remember he's wanted to be an elephant trainer. At twelve years old, he's the youngest - and in his eyes the best - elephant handler in his village. Tin can think of nothing he'd rather do that spend all day with his elephant, Lady, looking after her and playing together. But Tin's peaceful, idyllic life is changed dramatically when the Viet Cong attack his village and he finds himself held hostage by the terrifying soldiers who don't care if he lives or dies. Can Tin find the courage to escape from his captors and save not only his own life, but his precious elephants too?