Scotland Yard Investigator

Hoffmeyer immediately suspects the painting is a forgery after taking possession of it from Sam Todworthy. As an experienced art collector, he recognizes subtle inconsistencies that suggest the piece is not authentic. His suspicion is also a test, he wants to see if Collison's reaction indicates the National Gallery director was involved in a deliberate deception.

Earlier, Sam Todworthy had warned Hoffmeyer that the painting might not be genuine, planting the seed of doubt.

Sam Todworthy kills Anton Miran when Miran comes to reclaim the real Mona Lisa. Miran is connected to one of the Louvre men who originally handed Sam the genuine painting, and he demands it back. Sam refuses and murders him, hiding the body to eliminate a witness to his possession of the artwork.

After Sam offers to sell the real Mona Lisa to Hoffmeyer for £100,000, Hoffmeyer declines the deal and leaves the gallery. However, he then orders his men to kill Sam anyway, likely to eliminate anyone who knows the location of the real painting and prevent Sam from selling it to others or going to the police with evidence of the theft.

Sam's warning to Hoffmeyer earlier that the painting might be fake establishes Sam as someone who possesses knowledge dangerous to the thieves.

Hoffmeyer kills Jules when the henchman refuses to participate in the murder of Sam Todworthy. Jules balks at killing the art dealer, and Hoffmeyer executes him on the spot for insubordination. Jules's body is later discovered, triggering the Scotland Yard investigation that intensifies the pressure on all parties involved.

Toni advises her grandfather to contact the police when Sam offers to sell the real Mona Lisa back to the National Gallery. Though Collison is tempted to purchase it privately to avoid a scandal that would shock the French and the press, Toni recognizes that the situation has escalated beyond their ability to handle it safely and that law enforcement must be involved.

Collison refuses to reveal who currently has the real Mona Lisa because he fears that exposing the holder could cause a public scandal and endanger the artwork further. He prioritizes protecting the painting's safety over fully cooperating with the police investigation, creating tension with his granddaughter's fiancé Inspector Bob Cartwright.

Emma Todworthy arrives at Hoffmeyer's house during the confrontation between Collison and Hoffmeyer. She shoots Hoffmeyer in a desperate act of vengeance for the murder of her husband Sam. Hoffmeyer then stabs Emma with his sword, and both are mortally wounded in the struggle.

After the real Mona Lisa is recovered and taken to the airport for safekeeping with Professor Renault, the fake Mona Lisa is hung on Sir James Collison's wall as a memorial to the event. Years later, Collison sits beneath the framed replica and recounts the adventure to his great-grandson, turning the crisis into a family legend.

Hoffmeyer confronts Collison at the National Gallery after discovering the painting might be a forgery. He wants to determine if the gallery director was involved in the apparent scam, whether Collison knew the painting was fake and deliberately orchestrated the handover. Collison's reaction convinces Hoffmeyer that the director was not complicit.

Sam Todworthy, the art dealer, possesses the real Mona Lisa throughout most of the story. He received it from one of the Louvre men who originally handed it to him. While Hoffmeyer stole what he believed was the painting from the National Gallery, Sam held onto the genuine artwork and attempted to profit from it by selling it to various parties.

Scotland Yard's investigation begins after Jules's body is discovered. Inspector Bob Cartwright, who is also Toni's fiancé, leads the case. The investigation widens as Sam is murdered and suspicion falls on Hoffmeyer, but the investigation stalls at several points due to Collison's refusal to reveal the painting's location. The case ultimately concludes with the confrontation at Hoffmeyer's house.

Hoffmeyer uses a sword concealed within his cane during the confrontation with Collison at his house. He draws the sword to block Collison's attempt to retrieve the painting, creating a deadly standoff. When Emma shoots Hoffmeyer, he uses the sword to wound her fatally before Collison intervenes to prevent the painting from being destroyed.