Meet our plucky heroine, Miss Daisy Tannenbaum, almost 13, precocious as ever, and homeschooling in Paris with her Aunt Millicent. Daisy takes a break from Paris and her dreaded math homework and heads to a rambling chateau in the Loire to help her Aunt Mill's friend and fellow former spy, Felix, catalog his art collection. But when Daisy receives a copy of the Mona Lisa as a thank you gift from Felix, strange things start to happen. This Mona is not just any copy, it's one of two perfect forgeries created to fool the Nazis during their hunt for the real Mona Lisa in WWII. Daisy's best friend from the states, Lucia, a newly minted teen model in Paris to audition for the spring runway shows, thinks Daisy's Mona is the real one. Real or not, it's worth a fortune, and when Felix suddenly dies, his family accuses Daisy of stealing it. Daisy must navigate a world of crazy, scheming, frequently criminal adults, not to mention traveling ghosts, ginormous pigs, testy lawyers, former spies, and obnoxious fashionistas, as she finds herself trying to outwit them all to keep her beloved Mona and maybe even become a grande patronesse of the Louvre, the youngest one ever.