Leonardo da Vinci's Mona Lisa hangs in the Louvre as the most examined painting in the world, but a second canvas complicates the story. In 1913 a painting surfaced in England showing a younger, unfinished version of the same sitter, later named the Isleworth Mona Lisa, and this film follows the researchers trying to determine whether it is an earlier work by Leonardo's own hand or a later imitation. Experts compare brushstroke technique, pigment composition, and the underlying geometry of both paintings, and set the findings against historical records of Leonardo's commissions and known working methods. The investigation moves between conservation labs and archives, weighing physical evidence against the paper trail for a second commissioned portrait. The film treats the forgery question as genuinely open rather than settled, laying out what the scientific analysis can and cannot prove about authorship. It ends with the case for and against a second authentic Mona Lisa left for the viewer to weigh, rather than a verdict handed down.