The Medusa Plot (The 39 Clues

An explosive new series! After the mysterious Vespers kidnap a number of Cahills, they order Amy and Dan to steal a priceless painting in exchange for hostages. The siblings then rush to Italy where they arrange a heist that rivals the most famous art thefts in history. There's just one problem - the painting they steal is fake. With the clock ticking, Amy and Dan have to track down the real painting before one of the Cahill hostages is lost forever.