LONDON — It’s common to return a library book late — but not by half a century.

Staff at a British library say they were surprised and puzzled when they received a book that was 45 years overdue through their mailbox.

Alison Lawrie, the principal assistant at Dinnington Library, near northern England’s Sheffield, says the Penguin first edition copy of “Quatermass and the Pit” by Nigel Kneale was due back on Oct. 15, 1965.

She says the borrower remains a mystery because the library records don’t go back that far, and the sender didn’t attach a letter or note with the book.

Lawrie said Friday the sender need not worry about a hefty fine.

She says: “If the person who returned the book wants to come forward, we’d love to know the story behind it.”