“I would tell you, my lord,” Gideon promised, “if I had discovered anything that would do you good. Believe me, I have not.”

“I see.” Damien felt his pulse slowing, as it always did when he had to use force. The anticipation of violence had a calming effect on him — like a form of prayer. “That’s unfortunate, my friend. I don’t claim your skill with alchemy. But I do conduct my own research with mechanics, as you know. Unlike you, I have no problem testing my inventions on live subjects. Let me demonstrate.”

Damien stepped on the release switch, and the ceiling above Gideon collapsed.

It was one of Damien’s simpler creations but still impressive. The attic above the Vesper seal held three limestone columns set a hand’s breadth apart, each as thick and heavy as a ship’s mast yet perfectly balanced, so that only the slightest linchpin was needed to keep them in position. At the flick of a switch, gears turned, an iron rod retracted, and the Vesper seal crumbled. The columns crashed down like the fist of God.

The sound was terrible. The columns shattered. Shards of rubble flew everywhere, shaking the entire manor. Underneath the collapse, Gideon should have been smashed flat.

Yet when the dust cleared, Damien saw Gideon Cahill standing five feet behind the wreckage, unharmed except for scraped and bleeding knuckles on his right hand.

 My God, Damien thought. It’s true. Despite himself, he laughed with delight.

He realized his mistake too late. Gideon moved almost faster than Damien’s eyes could register. In a heartbeat, he had Damien pinned to the wall, his fingers around Damien’s throat. Damien was not light, but Gideon manhandled him as if he were a straw-stuffed scarecrow.

“You try to kill me, my lord?” Gideon’s eyes flared. “Then laugh about it?”

For a moment, Damien was too shocked to speak. Laying hands on a noble was punishable by death, and yet Gideon — the gentlest man Damien had ever met — seemed quite ready to break Damien’s neck. Gideon’s thumb and fingers pressed under his jaw. Damien’s pulse throbbed. His vision began to darken. With a flick of his wrist, he managed to slide a knife from his sleeve, where he always kept it.

“Is it — worth the price — Gideon?” Damien gasped, barely able to speak with his windpipe constricted. He pressed the tip of his knife gently against Gideon’s ribs. “Think carefully.”

Gideon’s grip tightened. His eyes were still full of murderous rage.

“We’ll die together,” Damien croaked. “But — won’t end there. Your mother — in Milan. Your brother — in Dublin. Your wife and children …”

Damien watched Gideon’s face as the meaning of his words sank in. It was risky, threatening an angry man, but Damien had to remind him whom he was dealing with. Damien’s network of spies and assassins extended far beyond Ireland. He had many friends and many more well-paid lackeys who would not take kindly to their patron’s death. Gideon knew that. If he killed Damien Vesper, the entire Cahill family would be wiped from the earth.

There was an urgent pounding on the door. Balthazar burst in, sword drawn. “My lord, is everything —”

“Stay your hand!” Damien barked. He fixed his eyes on Gideon. “Everything is fine — isn’t it, Gideon? A small disagreement. Nothing more.”

Damien counted to five, wondering if each heartbeat would be his last. Finally, Gideon’s angry expression turned to disgust. He released his grip and stepped away.

Damien sheathed his dagger.

He swallowed, struggling for composure. “You see, Balthazar? Now leave us.”

Balthazar looked at his master in disbelief, then at the gaping hole in the ceiling and the shattered ton of limestone on the floor, no doubt wondering how this constituted a small disagreement.

“Y-yes, my lord,” he stammered. He quickly retreated, closing the door after him.

Gideon kicked at the rubble, scattering mosaic tiles from the Vesper crest. “I once thought better of you, Damien. I thought we were friends.”

“But we are friends.” Damien spoke with more ease than he felt, knowing he must turn the situation quickly. “The columns were only a test that I knew you would pass. Tell me … how did you dodge them?”

Gideon balled his fists. “If you threaten my family again, if you lay a hand on them —”

“No, no, of course,” Damien said hastily. “Spoken in a moment of anger! But back to the point — no man is so agile. Your bleeding knuckles … you actually pushed one of the stones aside?”

Gideon still looked ready to attack, but his civilized nature seemed to be reasserting itself, as Damien had hoped. Given a choice, Gideon Cahill would almost always choose talk over violence.

“I deflected a column,” Gideon allowed, “barely. Or it would’ve crushed me.”

Damien shook his head in wonder. “You instantly assessed how the stone was falling — its mass, its momentum, how best to apply force to change its course —”

“A simple calculation,” Gideon grumbled. “You could do the math as well as I.”

“But not so quickly,” Damien said. “Not in a heartbeat. You demonstrated unnatural speed, strength, mental acuity…. What has changed you, Gideon? What concoction have you made?”

Gideon blanched. “How …” His expression hardened as the truth dawned on him. “Of course — Maria.”

“Do not be too angry with her,” Damien said. “She needed the silver. And her husband … well, he’s been a guest in my dungeon for years. She really had no choice.”

Gideon brushed the dust from his shoulders. “I should have known,” he said bitterly. “Even with me, you use spies.”

“Your mind is agile,” Damien said. “You have apparently found a way to increase your perception. But even this cannot change your fundamental nature, my friend. You are too trusting. You see the best in people. It is your most glaring weakness. Now tell me, what secret have you uncovered?”

Gideon glowered at him. “I once believed you supported my work because you wanted a cure for the plague — because you wanted to help your people and build a better world.”

“I do want a cure,” Damien assured him. “It might safeguard my own life, for one thing. It would also be a valuable thing to sell. But what you’ve discovered is obviously of even greater importance. As for helping the peasants out of the goodness of my heart — please! If the Black Death has taught us anything, it is that life is cheap.”

“It teaches us life is precious!”

“Bah. I am not interested in stopping death, only in … directing it. This cure of yours … well, it was potentially valuable, but now you seem to have stumbled on something quite amazing — something that could help me immensely. I am interested in weapons, my friend. Power! That is how I’ll build a better world.”

Slowly, Gideon’s face turned waxy with horror. Damien had seen that look before on the faces of his test subjects as it slowly dawned on them that they would never be leaving his workshop. “You are truly evil.”

“That goes too far, Gideon. Even for you. This alchemy you’ve discovered, the process for strengthening the mind and body — it could give me an army powerful enough to drive the English from Ireland at last. King Henry is old and weak. His lapdogs in Dublin have been powerless for years. With your formula and the weapon I’m working on, Gideon, I could invade England itself. And after that …” He swept his hand across his newly acquired map. “A whole world awaits.”

Deadly silence.

Gideon wrapped his bleeding knuckles in the hem of his shirt. His hands were beginning to shake. Damien made a note of that, as he might with a test subject. Perhaps a side effect of Gideon’s formula? He would have to find out.

“Damien, I’m going home now,” Gideon said. “I think you should return to the mainland in the morning. You’re no longer welcome on my family lands.”

Damien felt a twinge of regret. So this was what it felt like to lose a friend. Such conversations they’d had in better times! Such excellent dinners! Peasants were easy to replace. Gideon Cahill would not be.

“You’ve known me for ten years, Gideon,” he said. “Have I ever failed to get what I want?”

“Good-bye, Lord Vesper.”

“Before I am done, you’ll wish those stones had crushed you,” Damien warned.

Gideon met his eyes one last time, but his expression held no more anger — only disappointment — as if he dared to believe this break was Damien’s fault.

Gideon left without another word.

Damien cursed and overturned his desk. Secret reports and Leonardo da Vinci sketches fluttered through the air, slowly settling in the rubble of his limestone trap.

Damien had tried. Truly, he had tried to be reasonable. But sometimes even the best plans must change. Tonight, Balthazar might get to use his sword after all.

Gideon cursed himself for a fool.

He was well acquainted with Damien’s ruthlessness, but he still couldn’t believe his old friend had tried to kill him. Worse: Damien had tricked him into revealing his newfound skills. Gideon had had enough trouble keeping Damien in check the past ten years, quietly thwarting his efforts to gain power, using his influence to calm Damien’s tempers and spare the peasants from the worst of his wrath. Now Gideon’s new discovery had upset the balance. Far from being a gift, the serum could ruin everything.

Halfway across the beach, Gideon almost collapsed from a wave of nausea, worse than before. The side effects of the master serum were becoming more pronounced by the hour. He held up his hand, his knuckles still bleeding. A few minutes ago, he’d had the strength to crush stone. Now his fingers shook like an old man’s. The more he used his new abilities, the more he deteriorated.

He needed twenty-four hours more to complete his new variation of the serum. Perhaps this time the balance of humors would be correct, and Gideon could counteract the damage he’d done to his body … if he had twenty-four hours.

Why couldn’t Damien have waited another day before confronting him?

As the nausea passed, Gideon took a deep breath and tried to clear his thoughts. The morning was unseasonably pleasant. Waves washed against the rocks. Gideon could see the mainland clearly, but he knew that from the mainland, this island would not be visible.

He could not stand to think that this ancestral stronghold, a refuge for generations of Cahills, might soon be his grave.

A square mile wide, the island was shaped like a cupped hand, with a palm of meadows in front and a protective curve of sheer limestone cliffs along the back like a row of fingers.

Despite the island’s size and the height of its cliffs, a rare combination of factors made it nearly impossible to see from a distance — a trick of the light, the way the stone and shadows mixed together, the reflective quality of the cliffs throwing back the color of the sea. Gideon’s great-great-grandmother Madeleine, one of the last famous Celtic warrior noblewomen, had discovered this place quite by accident, and even though her descendants had studied science for generations since, none of them quite understood the optical illusion that caused the island to disappear.