Art critic Alastair Sooke investigates why paintings worth tens of millions of dollars keep vanishing from museums and never resurface on any legitimate market. The film centers on the unsolved 1990 Isabella Stewart Gardner Museum heist in Boston, where thieves dressed as police officers cut Vermeer's The Concert and Rembrandt's Storm on the Sea of Galilee from their frames, a case still open with a reward that has climbed into the millions. Sooke talks to investigators and figures from the art crime world, including the notorious thief Myles Connor, to work out who actually buys stolen masterpieces once they can never be sold or shown. The answers point less to criminal masterminds hanging paintings in secret vaults than to collateral used in drug deals and ransom schemes, and to a black market where a painting's fame makes it a liability rather than an asset. Sooke's own attempts to trace where the Gardner paintings might be now make up the film's closing stretch.