We analyze a case of plagiarism that appears in a work published in 1928 by Paul Appell (1855–1930) in the collection Mémorial des sciences mathématiques. Appell's memoir entitled Le problème géométrique des déblais et remblais contains a verbatim copy of several pages from a memoir published in 1886 by Albert de Saint-Germain (1839–1914). By tracing back Appell's last years, we have found historical evidences that might cast a shadow of doubt on Appell's full responsibility by the plagiarism that appeared under his name.