Gabriel picked up one of the bottles of pigment—Alizarin Orange, once manufactured by Britain’s Imperial Chemical Industries, now nearly impossible to find. Mixed with transparent blacks, it produced a glaze unique in its richness. Gabriel’s own supply was running dangerously low. The restorer in him wanted to slip the bottle in his pocket. Instead, he returned the bottle to its place and studied the floor. Scattered around the base of the trolley were several more evidence markers.

“We found broken glass there along with two small wads of cotton wool. We also found the residue of a liquid chemical mixture of some sort. The lab is still working on the analysis.”

“Tell your lab it’s a mixture of acetone, methyl proxitol, and mineral spirits.”

“You sound fairly sure of yourself.”

“I am.”

“Anything else I should know?”

It was Chiara who answered. “In all likelihood, your lab technicians will discover that the proportions of the solution were two parts acetone, one part methyl proxitol, and ten parts mineral spirits.”

The detective gave her a nod of professional respect. Clearly, he was beginning to wonder about the true identities of the two “art investigators” with friends at MI5 and Downing Street.

“And the cotton wool?” he asked.

Gabriel lifted a pencil-sized wooden dowel from the trolley to demonstrate. “Liddell had begun removing the dirty varnish from the painting. He would have wound the cotton around the end of this and twirled it gently over the surface. When it became soiled, he would have dropped it on the floor and made a new one. He must have been working when the thief entered the house.”

“How can you be sure?”

“Because a good restorer always cleans up his studio at the end of a session. And Christopher Liddell was a good restorer.”

Gabriel looked at the camera. It was attached by a cable to a large-screen iMac computer, which stood at one end of an antique library table with leather inlay. Next to the computer was a stack of monographs dealing with Rembrandt’s life and work, including Gustaaf van Berkel’s indispensable Rembrandt: The Complete Paintings.

“I’d like to see the photographs he made of the canvas.”

Harkness appeared to search his mind for a reason to object, but could find none. With Chiara peering over his shoulder, Gabriel powered on the computer and clicked on a folder labeled REMBRANDT, PORTRAIT OF A YOUNG WOMAN. Inside were eighteen photos, including several that had been taken after Liddell had begun the process of removing the varnish. Three of the shots seemed to focus on a pair of thin lines—one perfectly vertical, the other perfectly horizontal—that converged a few centimeters from Hendrickje’s left shoulder. Gabriel had encountered many types of surface creasing during his long career, but these were unusual in both their faintness and regularity. It was obvious the lines had intrigued Liddell as well.