Imagine discovering that obscure old books in your university library contained hidden messages.
Well, for regulars of the Weldon Library at Western University in Canada, the fantasy has just become a real-life mystery.
Assistant Professor Mike Moffatt was browsing the stacks on earlier this month, only to unearth an impenetrable coded message in one of the books on the third floor, leading to more than 15 discoveries in different texts.
Writing on his blog, he explains: "I was in the D.B. Weldon library at Western University on Sunday and discovered some form of cryptogram in one of the books in the 3rd floor stacks."
The book, called "International Economics: Trade and Investment", contained a white envelope and a plastic leaf.
"I opened the envelope and discovered the following note and plastic leaf. The leaf was not attached to the note in any way, I just placed it there," he wrote.
The 'Western University code': Can you crack it?
The majority of letters on the note were in black, except for a leaf which was green. They appeared to be colour printed.
"The physical leaf is made of plastic and has two paint splotches on it - one red, one cyan. I'm not sure what the grey pillow-shaped object is supposed to be," he wrote.
Since creating the post on 10 March, the assistant professor has received messages from other users who have made similar discoveries.
"I have two more of these notes I've found, see attached for photos. Unfortunately I don't have the title or page info where they were found," an email by a staff member at the library read.
"They're the same format - wingdings-esque font, special symbol in the code, small item contained in envelope, and larger image in bottom-left. They have the same URL on the back."
The discovery has sparked a real-life mystery at the library, with Mr. Moffatt offering $100 to anyone who can solve the puzzle.
"It's bugging the heck out of me," he wrote.
"Again, I will gladly pay $100 to anyone that can solve the mystery."
Since finding the first note, 17 more have come to light at the university. They have so far come in envelopes with an object in them - either a jewel, feather or leaf - that appear to contain some marking.
The notes contain roughly 50 symbols whilst the on the back of the notes, a reference to a blog is mentioned.
Each note appears to be colour printed and contains a picture of a household item such as a vase.
The earliest is from January 2013, but unconfirmed reports stretch back as far as two years ago.
"I keep hearing things like "sorry to disappoint, the notes don't mean anything, it's an art thing"," Mr. Moffatt said on his blog.
"That is certainly a strong possibility. I'm not sure why that should disappoint at all! I find the idea that these are a form of art really interesting. That still doesn't solve the mystery, though."
He added: "Who put them there? When were they put there? What was the artist thinking? How did they create the font? I have all kinds of questions, so if it is art, I'd be delighted if the artist stepped forward."