A quick link to an article on the theft of the Mona Lisa in 1911, an event alluded to at the start of ‘The Disappearance of Crispina Umberleigh’.

http://www.openculture.com/2019/02/how-the-mona-lisa-went-from-being-barely-known-to-suddenly-the-most-famous-painting-in-the-world-1911.html