“Why?” Gemma asked.

“It’s hard to explain. Aggie kept hoping that with enough time and encouragement, Penn would stop. Aggie believed that if we just loved Penn and tried to show her kindness, eventually Penn would come around. But nothing we said or did mattered to her. I think that was actually the beginning of the end for Aggie.”

“What do you mean?”

“Aggie’d never been as cruel as Penn, or even me,” Thea elaborated. “She really wasn’t cut out for the siren life. But she made do with it, killing only when she needed to and making it as merciful as she could. But Penn became relentless, and Aggie couldn’t live with it anymore.”

“But you could?” Gemma asked her pointedly. “All that senseless murder didn’t mean anything to you?”

“It’s not the same. You see the world in terms of one human lifetime, and you don’t understand the fragility of everything. You’re all going to die. Everyone will die quickly and easily. Illness, accidents, wars. It’s amazing humans live as long as they do. But I will be here for another millennium. I won’t turn my back on my sister for something that will be gone in the blink of an eye.”

“But Aggie did,” Gemma said.

“She’d always cared for human life.” Thea’s voice softened, the way it did whenever she spoke of Aggie. “Too much really. You’ll disagree, but when you’ve seen as much death as we have—not even from our hands, but by the hands of time—it begins to wear on you. So Aggie began looking for a way out, which Penn was angry about. It finally came to a head this summer.”

“Penn started going off the rails three hundred years ago, and it just finally got to be too much this summer?” Gemma asked skeptically.

“Aggie tried to change Penn at first, and when she realized that wasn’t working, she tried to look for a more peaceable solution. Like breaking the curse.” Thea motioned to Gemma then. “When she couldn’t do that, she finally said that’s enough.”

“You mean she told Penn to stop?” Gemma asked.

“Yes. She actually suggested that we all swim out to sea and starve ourselves until we died. Naturally, Penn disagreed, so Aggie threatened to run off right before a full moon, so we wouldn’t have a chance to replace her, and we’d all die that way.

“But I don’t think she really meant it. She was just provoking Penn, so she’d kill her. Aggie wanted her life as a siren to be over, and death was the only way she knew out of it.”

“If you both hated the way Penn was running your lives, why didn’t you and Aggie just stand up to her and stop her?” Gemma asked. “I mean, if it had gotten to the point where you had to choose between Aggie and Penn, why wouldn’t you choose Aggie?”

“They’re both my sisters,” Thea reminded her. “Our parents basically abandoned us. I’m eight years older than Penn.”

This admission surprised Gemma. She knew that Thea was the eldest, but she hadn’t thought it was by that much, since both Thea and Penn appeared to be around eighteen or twenty years old.

But then she remembered Penn saying that she’d only been fourteen when she became a siren. The curse apparently just made them appear to be in their sexual prime, and Gemma supposed that she looked around the same age, too.

“Eight years doesn’t sound like that much, but when we were young, it was a lot, especially when our mothers weren’t around,” Thea said. “So I raised them both as my own. It’s like asking to choose which one of my children to save. I couldn’t do it.” She shook her head. “I didn’t choose.”

“But you did,” Gemma persisted. “You turned your back on Aggie. You let Penn kill her.”

Thea didn’t disagree. For a moment she said nothing and just stared down at the floor. She wiped quickly at her eyes, but not fast enough to stop a solitary tear from falling down her cheek.

When she did finally speak, her voice was thick. “I never thought she’d actually go through with it. They’d been fighting for a while, but I never thought that Penn could really do it. Not to Aggie.”

“When she did, when you realized what Penn was capable of, why didn’t you kill her then? Penn has killed two of your sisters,” Gemma said. “Three if you’re counting Lexi.”

“I never counted Lexi as my sister,” Thea muttered.

“You know Penn will just keep killing,” Gemma went on. “If I don’t stop her, she’s going to eventually kill me, and Liv, and … you.”

“If she does, I would deserve it,” Thea replied softly. Then she shook her head and took a deep breath, erasing the sadness from her expression. “Anyway … that’s how we ended up here.”

“You mean, with me?” Gemma asked.

“No, here in Capri.” Thea gestured around her. “It’s all part of Penn’s scheme for revenge.”

Gemma furrowed her brow. “I don’t follow.”

“She blamed Bastian’s absence on Demeter,” Thea explained. “It was because of the curse that he couldn’t love her, and that was Demeter’s fault.”

“Why didn’t she just try going after Bastian?” Gemma asked.

“She did, at first,” Thea said. “But the longer she went without finding him, the more enraged she became. And while some of that rage would splatter on the humans around her, she focused most of it on Demeter.”