Mysteries at the Museum (2010)

S7E13 Dial M for Missing, $7 Renoir, Secret in the Attic

Don delves into an ancient book that might shed light on the baffling vanishing of the world's most renowned mystery novelist. He also discovers a Renoir painting thought to have been purchased for a mere $7, along with a police ledger revealing the story of a clandestine romance that culminated in murder.