Around this table, Olivia and Gideon had celebrated the birth of each of their children. To think that they might never be together again … He swallowed and braced himself for what he must do.

“Children, I need your help. We are in great danger. As you well know, I’ve worked many years attempting to find a cure for the plague. At first, I sought a way to kill the contagion. Then it occurred to me that perhaps the answer was instead to strengthen the body. If a man could be made more resilient, healthier, stronger in mind, body, and spirit, then perhaps the Black Death could not touch him. My approach had … unexpected consequences.”

Katherine held up her vial with new interest. “A serum of some kind? To strengthen the receiver?”

Gideon glanced at Olivia. Her eyes were full of warning, but it was too late to turn back now.

“I discovered the formula quite by accident,” he said. “In its combined form … it is very potent.”

Jane’s eyes widened. “You took it! You experimented on yourself. Last month when you were sick, it wasn’t an illness, was it?”

Gideon shook his head. “I was terribly foolish, Jane. It almost killed me and —” He stopped himself before he could complete that thought: and it still might. “But when I rose from my bed, I found I had changed. I was stronger. More agile. My mind had a greater capacity for numbers. My memory increased a hundredfold.”

“Excellent.” Luke hefted the vial, a greedy light in his eyes. “And this is the serum? How can we be in danger, Father, if you are giving us such power?”

“I am not giving you such power,” Gideon said. “What you are holding is not the completed serum. That is … not perfected yet.”

 As in fatal, Gideon thought bitterly, but he tried to keep his tone even.

“I am still working on the final variation of the formula,” he said, “but for now the master serum is far too dangerous, especially if it were to fall into the wrong hands.”

“Like Luke’s,” Thomas grumbled.

“Shut up, oaf!” Luke snapped.

“Children!” Gideon said. “Lord Vesper has guessed about the serum. He will stop at nothing to get it, and he cannot be allowed to have it. We have very little time.”

Jane frowned. “But Lord Vesper is your friend.”

“Foolish little sister,” Katherine said. “His Lordship is no one’s friend. He tolerates people as long as they are useful. And Father is very useful.”

It was bitter to hear this from a girl of fifteen — bitter to think she had such a cynical view.

“Sadly, Katherine is right,” he said. “Damien — Lord Vesper — has become too power hungry. He cannot be trusted or kept at bay any longer. Your mother and I feared this might happen, which is why I have divided my research. Each of you must guard the treasures I have given you — ingredients, tools, pieces of the formula. Your individual portions are not meant to make sense. I have intentionally obscured the means to re-create the complete formula. But taken together, reassembled properly with all thirty-nine ingredients, these treasures will yield the secret of the master serum. Until we can escape Lord Vesper’s reach —”

“Wait,” Thomas said. “What about these glowing vials?”

Gideon hesitated. His work was so complex few adults could understand it, much less children. But looking around at his family, he knew he owed them complete honesty. More than that, he realized with fierce pride that all of them could understand. As different as they were, his children were all brilliant in their own ways. All of them were at least as bright as he was.

“Each vial holds an incomplete version of the serum,” he explained. “Thinking of you children — how different you are and yet how gifted — is what inspired me to try the four-part approach. While the master serum is still imperfect, far too dangerous to take, the four strands separately are safe enough. Together, your four vials would re-create the master serum, but in an emergency, children — you might use your individual serums to give you strength, according to your natural talents.”

“Give us the master serum,” Luke said. “You took the risk and lived! Together, we would be unstoppable. We could overcome Lord Vesper easily.”

Gideon shivered. His son’s tone reminded him too much of Damien’s. He could not tell Luke just how dearly his rash decision to try the serum had cost him. The new outbreak of the plague had given Gideon a sense of urgency, made him disregard caution and rush his research.

 If I can save more lives, he had thought, it will be worth the risk.

Now he was paying the price.

“No, Luke,” he insisted. “As I told you, the master serum is much too dangerous. It is far too tempting for anyone.”

“Except for you,” Luke said.

“Luke!” Olivia chided. “Your father is trying to save our family as well as his work.”

“But he doesn’t trust us with his secrets,” Luke said. “You’ve put us in danger. You want our help. You owe us the full power of your serum.”

Gideon could see the other children tensing, watching this battle of wills. They had never seen Luke rebel so brazenly, but Gideon couldn’t feel anger, only sorrow. Luke was suspicious, grasping, perhaps a little too much like Lord Vesper — but if so, it was because Gideon had not been there for him. He had been so absorbed in his work he hadn’t been a proper father.

His children might be brilliant, but they were still children, even Luke. They were already scared. Gideon had to stay confident for them. He couldn’t tell them about the unintended consequences of the master serum, about his own rapidly diminishing chances at survival. Unless he had twenty-four hours to complete the next variation …

“Of course,” he agreed. “Children, I have complete faith in you. Working together, the four of you will do more than I ever could alone. You will perfect the serum and make sure it is used only for good. When the time is right, and you are far away from here, you can pool your resources and —”

“Where are we going?” Katherine interrupted. “And why are you talking as if you aren’t coming with us?”

Gideon forced a smile. “Of course I will come with you. But I want you all to get safely away first. Thomas, are the boats still in the cove?”

Thomas nodded, clearly mystified. Since the time of Madeleine, who’d discovered the island, all Cahills had been natural mariners. They learned to swim and navigate as soon as they could walk. The family kept three small boats on the far side of the island, ostensibly for fishing and amusement, but Gideon always felt better knowing they had a private escape route far from Lord Vesper’s docks.

“Tonight,” he said, “you will pack your things. Bring only essentials that you can easily carry — and of course the serums I have given you, well hidden in your bags. I will secure the laboratory to make sure none of my research falls into Vesper’s hands.”

“You mean you’ll destroy the research?” Luke asked incredulously.

“Listen!” Gideon insisted. “We must not give any sign that we are fleeing. We will cook dinner as usual and spend the night so Lord Vesper does not grow suspicious.”

“But why not leave now?” Jane asked.

Gideon glanced toward the house. In the window of the upper bedroom, the housekeeper Maria’s face hovered like a pale ghost, watching. She would not leave until nightfall, when she would return to her own cottage near Lord Vesper’s house. Five years she’d been with the Cahills … five years on Damien’s payroll of spies.

“We cannot give Lord Vesper any reason to suspect we are fleeing,” he repeated. “His guards on the island are more than capable of stopping us. And on the mainland … his reach is long indeed. We must get as far away as possible before he discovers our plan.”

“Just before dawn, then,” Thomas said. “That’s the next time the tides will allow us to leave safely, at any rate.”

Gideon nodded, grateful for Thomas’s practicality.

He didn’t add the last reason he needed more time. He had to continue his last attempt to perfect the serum. He might not succeed, but he had to try. And that meant he would have to stay longer than his family.

“In the morning, then,” he said, “just before first light, you will make your way to the boats and head to the mainland. I will stay behind and buy you as much time as I can. At my first opportunity, I will make some excuse to visit the mainland, then meet you on the road to Cork. By the time Vesper discovers we’re gone, we’ll be far beyond his reach.”

“But what if it doesn’t work?” Jane’s voice quavered. “What if Lord Vesper won’t let you go? What if Lord Vesper stops us and searches us?”

“It will work, my dear.” Gideon tried to sound reassuring. “I’m giving you the elements of the formula for a reason. Even if he found you, Vesper would probably never think to search you. He has no children and does not approve of children. I don’t think it would ever occur to him that you might hold something of value.”

No one argued this point. In all the years Vesper had been their family “friend,” he never seemed to remember the children’s names. To him, they were like cats — of some limited value, to be tolerated but not worth noticing, much less naming.

Olivia rested her hand on his arm. “Yes, husband. We’ll do as you say. Won’t we, children?”

They all nodded, though none of them looked comfortable with this plan, even Olivia.

“I can say no more for now,” Gideon insisted. “Go to your rooms. Be prepared to leave, but for God’s sake, children, be careful. Do not pack until Maria leaves for the evening. Do not say or do anything to make her suspicious.”

“But why?” Jane asked.

He cleared his throat. “Maria … Maria would worry if she knew. Now go. And guard these packages with your lives.”

To his relief, the children obeyed. Nervously, they clutched their newfound treasures and headed for the house in a group — looking for once like they had a united purpose.

Olivia turned toward him once they were alone. “Gideon, I don’t like this plan.”

“We agreed —”

“And I will support you, but there must be another way.” She rubbed her stomach as if it had begun to hurt. “There are … there are factors we haven’t discussed.”

Something in her voice troubled him. “What do you mean?”

“I just …” Whatever she was going to say, she apparently changed her mind. “We can’t simply leave this island for Vesper to take. It’s our home. It’s been your family’s home for generations. And the ring. I know you said never to speak of it, but —”

“I will send it with you to the mainland,” Gideon promised, though the idea chilled his blood. Olivia was the only person he’d told about the ring’s terrible secret, but asking her to carry that burden seemed unconscionably risky.