When Luna, a young caretaker at a cloning facility, falls for a defective clone, she must choose between completing her father's life work or helping the boy she loves to survive. After her parents' death in a terrorist attack, fifteen-year-old Luna escapes the pain by throwing herself into work at her father's hospital. In an experimental nursery, she meets the clone of a young boy whose heart will stop at the age of eighteen. The only hope for the original boy is if researchers flip the right genetic switch in a clone whose growth is accelerated from birth to adult in three months. The clone, Michael, is a wild, defiant child, but her father's partner discovers Luna is the only person to whom the Michael clones respond. After witnessing the twentieth clone die, a despondent Luna searches for a reason to continue to risk her heart. But the 21st Michael clone turns out to be more than Luna expects-more trusting, more alive, and more in love with her than the ones before. Unfortunately, their time together is running out. Luna vows to help him escape the sterile Institute to live his last day to the fullest before his heart stops. However, the person who can provide the tech she needs to escape is Jorge, the boyfriend she ran out on five years earlier, and he wants another chance to win her heart. Can Luna decide where her heart is leading her before time runs out?