If it hadn't been for Lucas's photographic memory, they might not have remembered the man. It had been almost a year since she and Kari noticed him copying a famous Rembrandt painting in the Minneapolis Institute of Arts. But now in the National Gallery in London, they spot the same guy, copying another Rembrandt. Then, when a never-before-seen Rembrandt painting is discovered in Amsterdam, the girls begin to suspect the truth. Convinced that no one will believe them without hard and fast evidence, the teenage sleuths embark on a madcap adventure to find the forger and bring him to justice.