Casso (Johnny Depp) is obsessed with collecting bizarre and rare books. This talent is greatly appreciated by the rich man Balkan (Frank Langella). He gave Casso a difficult task-to find an ancient book called "The Ninth Door" and to identify the authenticity of the one in his hand. There are only three copies of this book in the world, and the remaining two have been lost in Portugal and France respectively. Legend has it that as long as you read this book through, you can summon the arrival of the devil. Casso began a tortuous and magical search. He visited the wife of the original owner of the book, an expert in ancient book repair, and met a mysterious woman with green eyes. During this period, his friend's sudden death was exactly the same as the illustrations in the book, and murders were still being staged one after another. It turns out that the spell in the book may make the owner unsustainable. And if the three books are combined together, the evil Satan will be ushered in. In the end, did the devil's face appear?