Scotland Yard Investigator

Following the liberation of Paris in World War II, the Louvre administration initiates a plan to retrieve the Mona Lisa from the National Gallery's London vault. The authorities coordinate a cross-channel effort to move the painting back to France under safe conditions. This decision sets Hoffmeyer's later theft plot into motion.

Sir James Collison of the National Gallery in London and his granddaughter Toni discuss how to safely return the painting and manage the delicate transfer. They align on a plan to safeguard the artwork while ensuring its eventual return. Hoffmeyer's plot to steal it secretly begins to loom in the background.

Hoffmeyer enlists his two henchmen, Henri and Jules, to pose as Louvre officials arriving to collect the painting. He designs a theft scheme around the handover, counting on misdirection to seize the Mona Lisa. The scheme sets the stage for the ensuing crime.

The would-be thieves obtain what they believe to be the Mona Lisa, but Hoffmeyer immediately suspects a forgery after taking possession. He questions whether the London gallery directors are in on the scam. The discovery pushes the plot toward a direct confrontation with the gallery leadership.

Hoffmeyer confronts Collison at the National Gallery, exposing his suspicion that the plan is a setup. Collison's reaction suggests he was not involved in the scam, though doubt remains. The uneasy meeting heightens the tension between the thief and the gallery leadership.

Hoffmeyer suspects dealer Sam Todworthy of having the real Mona Lisa, and pays him a visit. Sam had warned Hoffmeyer beforehand that the painting might not be genuine. The warning adds a layer of doubt to the looming theft.

Prior to Hoffmeyer's visit, Anton Miran comes to retrieve the real painting from Sam. Sam kills Miran and hides the body, eliminating a potential witness and worsening the web of intrigue surrounding the painting. The act escalates the stakes for everyone involved.

Sam offers to sell the painting to Hoffmeyer for £100,000, but Hoffmeyer declines the offer. As soon as Hoffmeyer leaves the dealer's gallery, he orders his men to kill Sam and secure the painting. The price rejection triggers a murderous turnaround in the plot.

When Jules refuses to participate in the killing, Hoffmeyer kills him. A few days later, Jules's body is found, and Scotland Yard launches an investigation into the murder. The case widens the net of suspicion around Hoffmeyer and others connected to the plot.

Sam tries to re-sell the real Mona Lisa to the National Gallery, showing it to Collison. Collison is tempted to buy it to avoid a public scandal, but Toni advises him to contact the police. The tension between desire to protect reputation and legal duty sharpens the moral stakes.

Director Renault informs Toni that the two men sent to collect the painting have been kidnapped, and he will come to collect the painting in person. The kidnapping threat underlines the fragility of the operation and raises cross-channel urgency. The Louvre's direct involvement intensifies the crisis.

Toni confides in her fiancé, Inspector Bob Cartwright, who leads the investigation. Collison refuses to reveal who currently has the painting, arguing that exposing the holder could cause a public scandal and endanger the artwork. The stalemate heightens the suspense around the painting's fate.

Sam is murdered before either the police or Collison can intervene. With little evidence, Collison suspects Hoffmeyer of the crime, but there is no conclusive proof to pin on him. The murder closes one thread while opening another in the chase for the painting.

Collison sneaks into Hoffmeyer's house hoping to retrieve the painting. Hoffmeyer intercepts him with a sword drawn from his cane, leading to a deadly standoff. Sam's wife Emma shoots Hoffmeyer in vengeance, and Hoffmeyer mortally wounds Emma with a sword thrust; Collison intervenes to stop Hoffmeyer from harming the Mona Lisa.

Toni and Bob take the painting to the airport, where Renault awaits. The fake Mona Lisa is hung on Collison's wall as a memorial to the event, and years later Collison narrates the adventure to his great-grandson. The real painting's fate is secured, and the legend of the chase becomes a family tale.