The adventures of Country Mouse and City Mouse are set in the early 20th century. Emily, the practical country mouse, and her cousin Alexander, the urbane city mouse, visit endearing friends and relatives around the world, explore exotic locales, and experience thrilling and exciting adventures on their travels. Emily and Alexander are urgently called to Paris by their cousin Gaston, because strange things are happening in the Louvre. An unknown person is secretly painting mustaches on the famous paintings of the great old masters. Even the Mona Lisa is not spared. Emily, a country mouse, and Alexander, a city mouse, join Gaston in searching for the culprit. Their suspicions initially fall on a strange-looking man who is in the museum every day. As it turns out, it is the painter Claude Monet. So the search for the mustache painter continues.