The Mystery of the Third Lucretia — Susan Runholt

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 had noticed him copying the famous Rembrandt painting in the Minneapolis Institute of Arts. But now in the National Gallery in London, they're sure it's the same guy, copying another Rembrandt. What is going on?

The International Herald Tribune gives them their answer. A never-before-seen Rembrandt painting has been discovered in Amsterdam. The mysterious man must've been working on a forgery! Convinced that no one will believe them without more evidence, the teenage sleuths embark on a madcap adventure to find the forger. But is bringing the criminal to justice worth the price of their lives?