Newnham College, one of the women-only colleges of Cambridge, has uncovered an exam-time chocolate-smuggling ring operating out of the college library. A mysterious book found during a stock check had been hollowed out and filled with two hidden candy bars.

"Dear student, congratulations on finding this book. Take your prize and return with one for the next person," read the note at the bottom of the stash.

Food and drink aren't allowed in the library, so this is a nifty bit of mischief.

It could have gone entirely undiscovered, too, but the book—Margaret Drabble's Oxford Companion to English Literature—had no library labels on it, prompting a student library worker to open it up.

Cambridge News says it's not clear how many times the candy had been found and replaced over the exam period.

"We don't know how long the book was there for but we don't think it was very long. A lot of our students got firsts [on their exams] this year so who knows whether they were helped with their studies by these chocolates," said Newnham College spokeswoman Jo Tynan.

This isn't the first time Newnham students have hidden secrets in library books. When Tynan posted about the chocolate stash on the college's Facebook page, alumna told her they'd found a pack of Minstrels (chocolate candy) and a love letter in the stacks.

Finding the book would have been tough for anyone who didn't know where to look. The library is one of Cambridge's largest, housing 90,000 volumes.

[H/T Arbroath, Photo: Newnham College/Facebook]