Nineteenth-century psychiatrists believed a patient’s condition could be diagnosed by analysing their face. Théodore Géricault, master of French romanticism, was commissioned to paint 10 portraits but five went missing …

On a hot summer night in 2018, Javier Burgos stayed up late on his computer. His wife and daughters were already asleep when he decided to do another round of Google searches. This time the biologist’s quest to solve a century-old art riddle took him to a 2013 exhibition in Ravenna, Italy.

Burgos dully watched the first seconds of a video of the show when something caught his eye. When he paused the video, the still image showed a museum wall hung with two portraits. He recognised one of them, a 19th-century painting called Le Medecin Chef de l’Asile de Bouffon by Théodore Géricault, one of the masters of French romanticism. But the other portrait was new to him.