“Oleander poisoning?”

He nodded grudgingly. “A not unreasonable hypothesis. Many physicians would make the same mistake. But oleander induces retinal toxicity only in chronic cases.”

So the blue illusion must be significant, but it was a new symptom to me. I thumped my brain to spill out whatever it knew about diuretics and expectorants. Nothing relevant appeared, but Gerolamo the herbalist had mentioned a laxative that might be appropriate. I made a guess.

“Virgin’s glove?”

The Maestro’s nod of approval was intended to mask annoyance. His hands withdrew into his lap. “Very good! Continue.”

“Also known as fairy thimbles or witches’ gloves or foxglove. In his celebrated De Historia Stirpium Commentarii, the learned Leonard Fuchs named it digitalis.” Which was how it was labeled in the Maestro’s collection-so why had he sent me to buy more, and under another name? “As I recall the medical uses of foxglove, the fresh leaves, when bruised, are efficacious in the treatment of wounds and the juice is used to relieve scrofula. Internally it can be taken as a laxative, but is unpredictable and dangerously toxic. What treatment did you advocate?”

He pouted. “I suggested that his own physician be summoned at once, as he would be more familiar with the procurator’s regimen.”

The first treatment for suspected poisoning is to induce vomiting, but the patient had been retching spontaneously without ejecting any matter. A rapid pulse would suggest that the patient should be bled, but he was elderly and might have unknown ailments. Even sips of water might have been dangerous. The Maestro had diagnosed murder and seen his own danger; any advice he had given would have been suspect. I could not blame him for taking the path of caution in this instance.

“Can you estimate when the patient ingested the poison?”

He shrugged. “He had obviously not eaten recently.”

“You imply that he must have been poisoned after he arrived?”

“An obvious hypothesis. And whatever the toxin, it must be extremely potent to be concealed in a glass of wine. The learned Paracelsus wrote that anything is poisonous in sufficient dosage.”

Worse and worse. “So there is no hope of laying the blame on tainted food in his own household?”

“No, and he had certainly not been munching on a salad of oleander. The dried and powdered leaf of digitalis can be prescribed for internal use, as a laxative, and it is rumored to soothe a raging heart. Possibly he took an accidental overdose, in which case we need not fear a murder charge. The man’s doctor must be interrogated.”

I said, “He’s probably a Jew, in which case he has likely been arrested already. If I were one of the state inquisitors, I should now be putting Imer’s servants to the question, especially the footmen who served the wine.”

“But you are not!”

“Then why don’t you offer one of the servants an enormous bribe to run away and take the suspicion with him?”

He shook his head, still angry. “No, we can ignore the servants, so-”

“Why?”

The Maestro matched up his fingertips again for another lecture. “Why should an attorney’s footman want to murder a procurator? Only if bribed to do so by someone of high rank, and if he is fool enough to be still in the city, then the Ten can catch him and torture the truth out of him. The doge would not be warning me away if he expected that to happen. But even the Three will not question the gentry rigorously without good reason to do so, certainly not torture them. The courtesans may not fare quite as well as the nobility, but even they-”

“Courtesans?”

He pouted. “There were several there. Your friend was one of them. Is she capable of poisoning a man, one who insulted her, say?”

“Certainly. I’ll ask her if she remembers doing so.” Violetta is a neighbor and the most prized courtesan in the city. The lady and I are friends, but I do not employ her services. One night with Violetta costs more than I earn in a year.

The Maestro pulled a sour smile. “Then you now have two reasons to help me find the murderer. If I had the birthday and time of birth of everyone who was present, their horoscopes…but the law will require palpable evidence, either eyewitnesses or a confession.”

“Denizens of the infernal regions must know.”

“Don’t be absurd!” He glared at me. “Beg my life from a fiend? Don’t you hear anything I teach you? I can’t do that.”

He was hinting that I could. For me to try to save him would be altruistic and therefore less dangerous. Not safe, just less dangerous. Summoning is best done after dark, when demons are more active and there are fewer people around to catch you at it. I would decide then whether to take the risk.

I thought of another problem. “How much foxglove would be needed? And what does it taste like?” I rose to reach for the De Historia Stirpium Commentarii that lay on his side of the desk. “Would wine disguise its taste?”

“Sit down. You think I have not consulted the herbals? Most poisons are vile-tasting, as you know, because they are tainted by the Evil One. Foxglove is so bitter that livestock will not graze it, whereas they do die from eating oleander. The taste and dosage would depend on how the essence was extracted. Steeping in water may be enough, or spirituous extraction followed by reduction. I shall conduct some experiments.”

“If you have any sense at all,” I said, “you will throw your entire supply in the canal and destroy the label on the bottle. Yesterday you sent me out to buy every nasty thing in the pharmacopeia. Was that a wise action?”

He bunched his cheeks. “I wanted to discover if digitalis is presently available in the city. Since only the murderer and I knew the poison used, I preferred not to advertise its name.”

“Even if Gerolamo and the rest do not stock it, surely foxglove can be grown in any little garden plot. It likes sandy soil, as I recall.”

As a feat of memory that remark was pure show-off, and his wizened little eyes tightened to show that he knew it. “But that would still be evidence of premeditation.”

And oleander was common enough. “So anyone could acquire the plant. But who,” I asked innocently, “could possibly have the arcane knowledge to extract and concentrate the venom? Or is this where we began this conversation?”

The Maestro scowled, because Italians are notorious as the poison experts of Europe, the Venetian Council of Ten has the same reputation within Italy itself, and the Council of Ten has been known to consult Maestro Nostradamus on such matters. And that, I realized, might well be what it was up to in the present instance, except that it was putting the demand for assistance in the form of a personal warning from the doge. That would explain why Sciara had felt justified in dragging me off to jail.

I opened my inkwell. “You will, of course, now write to the Lion’s Mouth to report your suspicions that Procurator Orseolo died of an overdose of medicinal digitalis. You will have to sign it.”

The bocca di leone is any of several drop boxes available in the palace to accept accusations of treason or other major crimes. Anonymous tips are supposedly ignored, but no one believes that.

The Maestro grimaced. “No. I despise men who work in silence and darkness. Very few people could have committed the crime. It must be possible to work out which one did. Then we can report to the Ten.”

There is no use arguing with him when he sticks out his goatee like that. “We have two days.” The doge had given me three, but I was allowing one for travel. I opened a drawer and selected a quill and a sheet of our best rag paper. “The attorney, Imer, is the man to start with. He must be quaking in his dancing pumps.”

Maestro Nostradamus said, “Faugh! You still don’t know how bad this is. Take a cheaper sheet.”

I changed the paper.

“There were about thirty guests in all,” he said, “but not all are suspect. Only the procurator was affected, so the poison was not in the bottle. It must have been put in his glass. It acts quickly but not instantaneously-I know that but the Ten do not. So the only persons who matter are those who came in to look at the manuscripts.”