When his import/export business infiltrated by international diamond smugglers, Mr. Moto must follow a trail of clues littered with beautiful women, glittering gems and deadly assassins. Making his way from the mysterious streets of San Francisco's Chinatown to the dark and dangerous alleys of Shanghai, Mr. Moto will stop at nothing to bring the culprits to justice...even if it means making the ultimate sacrifice!

孤儿海蒂（Shirley Temple 秀兰•邓波 饰）和黛特阿姨（Mady Christians 饰）生活在一起，然而黛特不愿继续在照顾外甥女，于是千里迢迢将海蒂送到偏远的善终——海蒂爷爷（Jean Hersholt 饰）的隐居之处。因失去儿子而沉浸悲伤之中爷爷阿道夫 起初无视这个从未见过面的孙女，但随着时间推移，祖孙俩的感情日益加深。
但是贪婪的黛特再次返回，骗走海蒂欲将其卖给他人作女佣。天使般的海蒂和主人家的病弱女儿安娜（Helen Westley 饰）培养出亲密的友情；另一方面，阿道夫也踏上寻找孙女的旅程……