Allie's communications chip told her she had an incoming message from Col about the AI's radiation scan. Not wanting to bother Galen with it, she headed for the living room so she could put the map up on the wall screen.

"How many locations?" Allie asked, pulling on some pants.

"Four point sources, plus three travel paths," the AI replied.

"Where is it now?" She clipped her bra.

"Unknown. No current radiation signatures match the profile."

Allie swore. That didn't make sense. Unless the plutonium was well shielded. Maybe their amateur was only pretending not to know what he or she was doing.

"Show me all the locations," she commanded, reaching for her shirt.

Half the Colony lit up. Three spots in Metropolis, plus one in the Aqua Dome, and a blue beam connecting them all and the route to Ira's office.

"Remove the travel routes," she said, savagely twisting the buttons as she fastened her shirt.

The beams vanished, leaving four blue blotches. "Zoom in to the site in Metropolis."

Allie blinked as the overlapping blotches separated into three different sites within the Maintenance building. A storage room, the workshop, and...no, that couldn't be right.

"Check again, Col," she ordered.

Her heart beat faster at the sight of Galen wearing nothing but a low-slung towel, but she fought to ignore it. She'd love to take him back to bed and not have to go to work, but this was too important. She'd planned on telling him the truth this morning anyway, so it was time to steel her heart against the inevitable rejection she'd suffer when he found out about her past. First, she had to find the remaining plutonium and ensure the safety of the Colony. Then she could hand him her heart so he could blow it to bits.

She almost broke her resolve when he kissed her cheek. It would have been so easy to turn her head and offer him her lips instead. She forced herself to focus on the screen, though it showed nothing of interest right now.

Allie didn't allow herself to relax until the hatch had slid shut behind Galen, sealing him out of her life. While the AI completed its scan, she reached into the refrigerator for a snack. Sven had given her enough fish for a week, and her mouth watered at the thought. It had taken almost all of her self control last night not to strip off and join the other Mer as they caught their dinner fresh, but Galen would never have understood. And she'd wanted one more night with him...so the small sacrifice had been worth it.

The scan still wasn't finished, so Allie reached for another fillet. It sure beat ration bars.

"Scan complete. Additional source identified," the AI said.

"Where? Show me."

Allie's heart contracted in her chest as the map showed her the Maintenance building again. "Show me the building in 3D, as it is now."

"Additional source has disappeared."

Allie swore. "Show me where it was."

A blinking blue light appeared, almost directly on top of another spot dated several weeks previously. Allie was afraid to ask, so she looked for the other sites next. One was in a supply room, and the other was in the workshop. The radiation source in the supply room had sat there for weeks, since before the Colony was inhabited. Whoever had planted it had to have been on the construction crew, or it had arrived with the supplies. The workshop had seen a radiation source several times over the weeks they'd lived in the Colony. Whoever had carried it there was definitely a resident.

"Show me radioactivity in brightness levels," she said.

The spot in the Aqua Dome dimmed to about half what the others were. All except the additional source Col had found today.

She couldn't avoid it any longer. Weeks ago, before the source had moved to the workshop, it had sat in one spot, almost exactly where it had briefly sat today. It shouldn't be possible, but Allie had to believe it was. Whoever had built the original bomb had only taken half of their plutonium to the Aqua Dome. And they still had the remainder, ready to blow this place sky high on a whim. She wouldn't let that happen.

Allie summoned a skimmer and climbed numbly onto the footboard. She missed the warm, solid feel of Galen standing behind her, but she needed to forget all that now. Forget her feelings, forget everything she loved about him, and focus on what was important.

It was far too short a trip to the Maintenance building in the bowels of Metropolis, but Allie told herself it was for the best. Logic told her she should call the Watch for backup, but she dismissed that idea. She could handle one man on her own. Once she'd found out what she needed to know, THEN the Watch could have him.

She strode into the building with a confidence she didn't feel, not today. She didn't slow until she reached the entrance to the office she was after. Then, she paused in the open doorway, wishing she was wrong, but knowing she wasn't.

"Why did you do it?" she asked.

No answer. Galen kept his eyes on the screen in front of him, ignoring her.

"I asked you why you did it. I saved your life. I have a right to know."

His lips moved, and he started singing faintly. Still he ignored her.

Allie noticed his peculiar ear coverings, with which he somehow blocked out all sound, including her voice. That's how he'd survived the Poseidon. He'd never heard her song, never fallen asleep like the other passengers, which is why he'd made it to the lifeboat when the alarms sounded, because he had heard those. She should have sunk the lifeboat while she had the chance, all those years ago.

"Allie!" With a practised motion, Galen pulled his headphones down so they circled his neck. His smile died as he took in the tears streaming down her face. "What's wrong, sweetheart?"

She was not sweet. Allie surveyed the desk. Where the blue spots had glowed, now she saw only a box for a residential pump. The same sort of pump she'd found hollowed out and full of explosives in the Aqua Dome main pumping station. "It's in here, isn't it?" She reached for the box.

So did Galen, but she was faster.

"Don't, sweetheart. It's dangerous. One of the other guys found it in the Arbor Dome main pumping station, where – "

"Don't lie to me." She lifted the box lid, and felt a surge of triumph as she saw another box, and not a pump, inside. She opened the box, peering in just long enough to confirm that she was right, before she threw the whole thing back on Galen's desk. "I had to see it for myself, or I wouldn't have believed it. I saved your life. I helped you. I stood up for you against the Watch, when they would have...not that it matters now. I can admit when I'm wrong. When I've been so stupid, so blinded, by the man I thought was my friend."

Galen stared at her. "I am your friend. More than that, if you'll let me. Allie, I – "

"I don't want to hear it," she snapped. "All I want to know is why. Why you did it."

Still he stared, as if he didn't understand.

"You planted that bomb in the pumping station. You built it. You nearly nuked the whole Colony with all of us in it. I want to know why."

"I..." Galen swallowed. "It was an accident."

Allie snorted. "Stardust."

"It was!" he insisted. "I built the bomb, sure, and I planted it. I only took half the plutonium because I thought it was uranium, and I wouldn't have enough for it to reach critical mass. I calculated the explosive charge perfectly. It would have damaged the pumping station, but left the dome structurally sound, and contaminated it with enough radiation to make it look like she did it."

"Like who did it?" Allie demanded.

"Halcyon. The siren who killed my parents, sank the Poseidon and murdered thousands of other people."

Allie bit her lip. "Fifteen hundred and sixty-two. Not thousands. And every single one of those was killed in an act of war. They were not civilians."

"She murdered more than a thousand people. Including my parents. They deserve justice."

Allie shook her head. "It's not murder when military personnel are killed in battle. Even if it was, the peace treaty signed by both Humans and Titans declared a general amnesty so no one on either side could be accused of war crimes once the treaty was signed. Anyone who killed or tortured was absolved of their guilt, so that all the atrocities would stop. It was the price we had to pay for peace."

"Not me. I didn't choose it. I wasn't the only one, either. The Humans First organisation offered to help me find her."

"They're nothing but a bunch of suicide bombers, and the racist bigots who recruit and arm them. They wanted you to blow yourself up with thousands of innocent civilians, and you nearly did." Tears formed in Allie's eyes again. "You almost destroyed all chance of peace between our peoples, and for what? One woman?"

Galen wet his lips. "Allie, I – "

"Then take your shot, Human." Allie threw her arms wide. "Your search is over and no one else needs to die. Enough people have been hurt. I lost the man I loved and gained a psychotic stalker. Where's the justice in that?"

She took pity on Galen's confusion. "I'm Halcyon. I killed all those people, including your father, Doctor Claudius Tasker, the man who lured my husband into a trap by promising to share his scientific findings, then tortured him to death before my eyes. He deserved to die, so I made sure he did. And crazed with grief, a siren's grief, which you can't even begin to understand, I sang his funeral dirge. A song that drove whoever heard it to die. Your music machine saved you, so you never knew what killed them. Every Titan knows what a siren is capable of, which is why they don't harm us. That's why the Mer are all pacifists, serving as mediators in a conflict because if Mer fight, only they will win. We know that, so we abstain. We tried – the Mer Council decreed that we'd take no part in the war – but Humans didn't listen. They captured my husband and tortured him for information. When they attacked him, they attacked all the Mer. So my people gave me permission to retrieve him, or seek justice as I saw fit."

Allie sucked in a deep breath, swiping at her tears. Now was not the time.

"I saw the torture chambers. Ceyx was killed in one, but there were many others, and they all showed signs of use. Prisoners were kept on Human ships and interrogated under torture before they were killed. I saw the mutilated bodies, and made sure their tormentors suffered. So I knew, when we declared that amnesty, that I had at least brought some to justice. I came to realise that the only way to stop Humans from torturing Titans was to either kill them all or end the war, and to that end, I agreed to mediate the treaty. I am the only living Mer to have gone to war, and Titans remember the stories. They know who and what I am, and they fear me because of it. It's only Humans like you who think I need something as crude as a weapon to destroy this place. I am a living weapon, but I will not be used against my people.

"So kill me now, if you must. I will die for the sake of peace, to keep you from killing anyone else. I'm no innocent. I have the blood of hundreds on my hands. There is no one left who loves me enough to mourn me, and the Mer have sworn they will not avenge me. So kill me."

Still Galen stared at her. "Allie, I...Halcyon." He swallowed. "I can't."