Sherlock Holmes and Dr. Watson find themselves in 1890s London in this holiday special.

亚茨拉斐尔（迈克尔·辛 Michael Sheen 饰）是守卫城门的天使，而克劳利（大卫·田纳特 David Tennant 说）则是堕落的恶魔。两人几千年来都一直隐姓埋名生活在人间，并且通过不断的尝试，在天堂和地狱之间建立了井水不犯河水的互惠互利的关系。
克劳利奉撒旦之命，将婴儿敌基督送到修道院，同美国外交官的新生儿做交换，当敌基督长到11岁时，就是世界末日来临之时。为了防止世界被毁灭，亚茨拉斐尔和克劳利决定通过影响这个孩子的善恶观念来避免世界的终结。在努力了11年之后，两人震惊的发现，他们竟然弄错了对象，而真正的敌基督此时生活在一个名为塔德菲尔德偏僻小镇中。

Mere seconds before the Earth is to be demolished by an alien construction crew, Arthur Dent is swept off the planet by his friend Ford Prefect, a researcher penning a new edition of "The Hitchhiker's Guide to the Galaxy."

When a chance encounter brings soldier John Watson into Sherlock's life, it's apparent the two men couldn't be more different, but Sherlock's intellect coupled with John's pragmatism soon forges an unbreakable alliance as they investigate a series of baffling cases together.

A Royal scandal, a dazzling game of cat and mouse. The seductive Irene Adler is cold, calculating, brilliant. Has Sherlock finally met his match?

Sherlock is back, but will things ever be the same again?