He must never touch the hands of the clock. He must master his anger. He must never, ever fall in love.

Jack is born with his heart frozen solid on the coldest day in history. A wise midwife saves him by replacing it with a cuckoo clock. Now Jack must abide by three rules to keep his mechanical heart safe: never touch the clock's hands, master his anger, and never fall in love. He tries his best, but when he meets a girl named Acacia he falls in love, threatening the delicate balance of his artificial heart.