A sealed envelope is an enigma containing further enigmas. This particular one was of the large, bulky manila variety with the name of the laboratory stamped in the lower left-hand corner. And, as she weighed it in her hand whilst scrabbling for a paper knife amongst the many brushes and bottles of paint and varnish, Julia could never have imagined the extent to which the gesture of slitting it open would change her life.

In fact, she already knew what the envelope contained. Or, as she discovered later, she thought she did. Perhaps that’s why she felt no special sense of anticipation until she’d removed the prints from the envelope, spread them out on the table and looked at them, almost holding her breath. Only then did she realise that her work on The Game of Chess would be far from routine. Unexpected discoveries, in paintings, on furniture, even on the binding of antiquarian books, were commonplace in her profession. During her six years of restoring works of art, she’d uncovered her fair share of preliminary sketches and pentimenti, of retouching and repainting and even forgeries. But never had she come across an inscription concealed beneath the painted surface of a picture: three words revealed by X-ray photography.

She picked up her crumpled pack of unfiltered cigarettes and lit one, unable to take her eyes off the prints. Given the evidence of the 12 x 16 inch X-ray plates, there was no possible room for doubt. The painting was a fifteenth-century Flemish panel, and the original sketch, done in grasaille, was as clearly visible as the grain of the wood and the glued joints of the three pieces of oak that made up the panel on which, out of lines, brush strokes and layers of underpaint, the artist had gradually created his work.