“Yes. And I wore gloves. Then and now. And the shoes were in a sealed evidence bag.”

“Still, there is obvious contamination.”

“If I am responsible for this, then I’m sorry. But I do not believe I am.”

Beatrice turned her round, stony face his way.

Rhyme saw the dismay in the young man’s eyes. Lesson delivered. “It’s not the end of the world, Ercole. The problem will be at trial. A defense lawyer could get the evidence from the shoe thrown out on those grounds. But we can ignore it for the moment. Our goal is to find him. The contamination’ll be the U.S. attorney’s problem at trial in the Southern District.”

Spiro chuckled. “You mean, Lincoln, it will be my problem in the Tribunale di Napoli.”

Rhyme shot him a wry look.

The Wolf Tits Rule…

Reading again, Rhyme said, “Now, those triacylglycerols, free fatty acids, pigment.”

Ercole said, “Beatrice has provided a chemical chart here. Should we write that down?”

Rhyme glanced at the molecular diagram. “No, not necessary. We’ve got what we need. Triacylglycerols—or triglycerides.”

“What are they?” Spiro asked.

“Fat basically. They’re energy reserves for living things. Molecules that contain glycol and three fatty acid chains. Hence, tri-glyceride. They’re found in both plants and animals. But animal fats tend to be saturated.”

“What does that mean?” Rossi made this inquiry.

“In a nutshell, saturated fats—the bad ones, if you listen to the health-minded—are so named because their carbon chains are saturated with hydrogen. This makes them more solid than unsaturated fats, which have less hydrogen.” He nodded at the diagram. “These are missing some hydrogen and therefore it is a plant fat.”

“But what kind?” Ercole asked.

“The sixty-four-thousand-dollar question.”

“The…what? I am not understanding,” Beatrice said.

“American cultural reference from a long time ago, fifty, sixty years or so.”

The officer translated for Beatrice, who gave a rare smile and said something, which Ercole translated: “She said that is not so ‘long ago,’ compared with cultural references in Italy.”

Sachs laughed.

Rhyme said, “We need to find out what plant. Is there a database of plants in the Scientific Police?”

Beatrice’s response was that there was one in Rome. She would go online and search it. She typed and spoke to herself as she did so. “Allora. A triglyceride molecule, unsaturated, una hydrocarbon chain, twenty-two carbon atoms in way of length. Dark green, the pigment. What plant, what plant…?” Finally she nodded. “Bene. I have gotten it. But helpful, I am not thinking so much. It is olive oil.”

Rhyme sighed, then glanced at Rossi. “How much olive oil would you say is produced in Italy?”

The inspector, in turn, handed off to Ercole. This would be, of course, his area of expertise. The young officer answered, “About four hundred and fifty thousand tons every year. We’re the world’s second-largest producer.” He grimaced and added defensively, “But we are closing in on Spain.”

How helpful is this? Rhyme thought, irritated. It could have come from anywhere in the country. “Hell.”