A favorite destination—even for New Yorkers—is the venerable Metropolitan Museum of Art. On this particular day, “the Met,” as generally known, experiences an unusually large number of visitors. Visitors have their choice of viewing over two million works of art spanning five millennia of cultures worldwide. But some among them are up to something more sinister.

At one point, the Met’s surveillance cameras’ lenses capture “a mysterious-looking couple” amid the many visitors strolling about the many galleries. The pair is dripping wet in their matching taupe Burberry trench coats. Just as the two of them walk past Soleil dans le Ciel de Saint-Paul, a masterpiece of Marc Chagall, a large tourist group—who, oddly enough, all are wearing distinctive red-and-white-striped vinyl raincoats—converges around them. But it is what happens next that baffles the museum’s surveillance crew. After “the mysterious-looking couple” pulls off their prank, they and the large tourist group walk out of that particular camera’s range, becoming submerged elsewhere in the interminable galleries of the gigantic museum.

But when a docent notices “something strange” with Chagall’s Soleil dans le Ciel de Saint-Paul, in short order, the museum-goers inside the Chagall gallery hear “High Alert!” and watch in horror as a heavy metal grille drops down from the ceiling to the floor, effectively locking them inside the gallery.

And thus began what later came to be called The Mysterious Affair at the Met.