“Ah, I see, then,” he said, and fell silent. “Perhaps,” the apothecary said after a few moments, “I should speak to him.”

“Is it your impression that he will attend, if you do?” Grey’s question held as much incredulous derision as curiosity, but Finbar Scanlon only smiled, and stretched himself again, the muscles of his forearms curving hard against the skin.

“Oh, I do, yes, sir. Mr. Trevelyan has been kind enough to say as he considers himself within my debt—and so he is, I suppose.”

“That you have come to nurse his wife? Yes, I should think he would feel grateful.”

The apothecary shook his head at that.

“Well, maybe, sir, but that’s more by way of being a matter of business. It was agreed between us that he would see to Francie’s safe removal to Ireland, money enough to care for her and the babe until my return, and a sum to me for my services. And if my services should cease to be required, I shall be put ashore at the nearest port, with my fare paid back to Ireland.”

“Yes? Well, then—”

“I meant the cure, sir.”

Grey looked at him in puzzlement.

“Cure? What, for the syphilis?”

“Aye, sir. The malaria.”

“Whatever do you mean, Scanlon?”

The apothecary picked up his cup and gulped beer, then set it down with an exhalation of satisfaction.

“’Tis a thing I learned from the surgeon, sir—the man as saved me life. He told it me while I lay sick, and I saw it work several times after.”

“Saw what, for God’s sake?”

“The malaria. If a man suffering from pox happened to contract malaria, once he’d recovered from the fever—if he did—the pox was cured, as well.”

Scanlon nodded to him, and lifted his cup, with an air of magisterial confidence.

“It does work, sir. And while the tertian fever may come back now and then, the syphilis does not. The fever of it burns the pox from the blood, d’ye see?”

“Holy God,” Grey said, suddenly enlightened. “You gave it to her—you infected that woman with malaria?”

“Aye, sir. And have done the same for Mr. Trevelyan, this very morning, with blood taken from a dyin’ sailor off the East India docks. Fitting, Mr. Trevelyan thought, that it should be one of his own men, so to speak, who’d provide the means of his deliverance.”

“He would!” Grey said scathingly. So that was it. Seeing the scarified flesh of Trevelyan’s arm, he had thought Scanlon had merely bled the man to insure his health. He had had not the faintest idea—

“It is done with blood, then? I had thought the fever was transmitted by the breathing of foul air.”