A copy of the top-secret storyline was found in the British cafe by a fan, after film bosses stopped for lunch and forgot to take the important document with them.
However, the finder - who is a huge fan of the $2 billion pirate film franchise - refused to look at the document because he wanted to watch the latest adventures of Captain Jack Sparrow, played by Johnny Depp, when it's released in May next year.
He told The Sun newspaper: "I resisted the urge to have a read. I want to enjoy the movie when it comes out."
Filming of the highly-anticipated fourth movie started in Hawaii June 21, '10, and follows the dishevelled pirate on his search for the Fountain of Youth.
After discovering the 194-page documents, the man handed them into the British publication, which returned them to Walt Disney Pictures - who are financing the film.
The film will also star Penelope Cruz as Angelica, an exotic beauty from the hunky pirate's past.
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