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

Jack and the Cuckoo-Clock Heart

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.