Two leather-bound notebooks written by the naturalist Charles Darwin (1809-1882) have mysteriously reappeared at the University of Cambridge, twenty-two years after they went missing. The notebooks are now worth many millions of pounds.

“I feel joyous,” said Dr Jessica Gardner, the university’s librarian. “They’re safe, they’re in good condition, they’re home.“

Dating from the late 1830s, the seminal works were produced by Darwin when he returned from his famous trip to the Galapagos Islands where he first began to develop his theory of evolution. Illustrated on one page is a rudimentary “tree of life” drawing from 1837, which helped inspire his groundbreaking work published more than twenty years later On the Origin of Species (1859).

“Objects such as these are crucial for our understanding of not only the history of science but the history of humankind,” explained Professor Stephen Toope, the vice-chancellor of the university.

The postcard-sized manuscripts were anonymously abandoned on the library floor in a vivid pink gift bag. In this bag was a large brown envelope bearing the brief message: “Librarian, Happy Easter X.” Inside this envelope was the museum’s original blue box containing the missing notebooks, tightly wrapped in cling film.

Although there is no CCTV of the immediate area where the notebooks were left, the Police are surveying all footage from nearby entrances and exits to track down the elusive “thief”. Much to Gardner’s dismay, the package was retained by police for five long days until it was finally released back into the care of the library for confirmation of authenticity.

“The notebooks can now retake their rightful place alongside the rest of the Darwin archive at Cambridge, at the heart of the nation’s cultural and scientific heritage, alongside the archives of Sir Isaac Newton and Prof Stephen Hawking,” remarked Gardner.

Cambridge University last had the notebooks in their possession in November 2000, when they removed them from the library’s special collections strongroom to be photographed. A routine check discovered they were indeed missing and presumed misplaced two months later, but they were not reported as stolen until 2020. Thereafter the BBC highlighted the lost works and the library launched an international appeal to locate them.

A Cambridgeshire constabulary spokesperson commented: “Our investigation remains open and we are following up some lines of inquiry. We also renew our appeal for anyone with information about the case to contact us.”

The peculiar incident has both baffled and delighted university employees, who intend to put the remarkable notebooks back on public display from July 2022.