Never underestimate a librarian.

Fifty-something Edinburgh librarian Shona is a proud former pupil of the Marcia Blaine School for Girls, but has a deep loathing for The Prime of Miss Jean Brodie, which she thinks gives her alma mater a bad name. Impeccably educated and an accomplished linguist, mathematician, martial artist, and musician, Shona is selected by Marcia Blaine herself to travel back in time for a crucial mission in Venice.

Finding the city afflicted by what appears to be a new outbreak of the plague, Shona soon encounters the Cornetto family of gondoliers. Lately, a number of their passengers have met a watery fate. Coincidence? Unlikely. She dons a mask, goes undercover and seeks inspiration in the library.

But the mystery only deepens. Why do the Cornettos seem so flaky and their explanations wafer-thin, even as they proclaim their innocence? What is going on at the printworks? Shona's powers of deduction, dissection and prowess as a swimmer are put to the test as she realises that a bitter feud is at play.

Can Shona unravel the tapestry of lies and get to the truth? It's a race against time, but it would be a mistake to underestimate a librarian.