Harriet turned the handle, opening the door just a crack, and peered into the laboratory.

“It’s all right, Cap’n,” Annabel said, removing her goggles and straightening up in front of the elaborate apparatus occupying most of the room. “You can come in. In fact, you’re just in time. Grab this for me, will you?”

Annabel held out a rubber tube which extended from the complex of copper pipes, glass flasks bubbling with colored fluids, pressure dials and clockwork mechanisms. A rubber bulb was fixed at the end of the tube. Looks like she’s nicked it from a bicycle horn, Harriet thought.

“Take this,” Annabel said. “And watch that dial there. No, the one on the right. That’s it. When the red needle points to zero, squeeze this and keep squeezing until I say stop. Ready?”

“I reckon,” Harriet said, smiling at her scientosophist-in-residence. “What’ll it do? I already lost one ship. Don’t want to go blowing up another one.”

“This won’t explode. I hope. But it should tell us what’s poisoning the city.”

“You mean, what’s causing the plague?”

“Exactly.”

“Blimey.”

“Blimey indeed, Cap’n. And once we know what’s causing it, then maybe we can do something about it.”

Confined to the ship, Harriet had been feeling restless. She was eager to get to the bottom of the mystery; to find out what was causing the foul malaise which had laid waste to Lundoon in the time she’d been away in the Outer Archipelago.

Harriet and the crew had felt a surge of excited anticipation when they’d caught sight of Earth, and their native city appeared through layers of cloud and smog. It had been five years since she and Sibelius set off from the Moon. She shook her head in wonder when she thought of the thirteen year old girl she’d been when she undertook the voyage.

It was a different Harriet, she knew, who had returned after all that time to find the city recovering from a civil war. And it was a different city waiting to greet her. The aftermath had left behind not only a dangerous anarchy, but a more mysterious and deadly threat.

In the grip of an incurable plague, half the citizens were frightened to leave their homes. The other half remained outside, their skin blistered by seeping boils, bodies wrecked by sickness and disease, to face an inevitable death.

Those Up-Toppers wealthy enough, and whose towers were not yet razed to the ground by the revolutionary group calling themselves The Topplers, had either fled the planet altogether or retreated behind locked gates and electrostatic fences. Although the plague had brought an end to the conflict, the towers resembled military fortifications more than the elegant emblems of wealth and cultural sophistication they had once been.

Sibelius, astonished to find his balloon both intact and still moored to one of the few remaining towers, had set off to find out what had happened to the Monkey Nation. That had been a week ago, and as much as she was certain he could look after himself, she was still anxious. There had been no news from him since he’d left.

But the worst of it was what had happened to Davy. He showed the early signs of the disease: blotchy skin, drowsiness followed by sudden fits of anxiety, and a loss of appetite. It had broken Harriet’s heart to give the order to confine him to his bunk.

She’d thought of abandoning Earth altogether. There was a whole world out there in the Dark Sea still waiting to be explored. But without Sibelius, and with Davy still sick and no known cure, that just wasn’t an option.

“Cap’n! Harry?” Annabel’s voice dragged her back from her thoughts.

“Yeah, sorry Annie,” Harriet said, forcing herself to concentrate. “I was just…”

“I know,” Annabel said. “Are you ready? When I say now, you squeeze. Get it?”

“Got it.”

“Good.”

Harriet held the tube in one hand and the rubber bulb in the other. Annabel pushed her hair back behind her ears, wiped her hands on her dress and shook the tension from her fingers.

“Right,” she said. “Here we go. On the count of three. One.” She opened a valve and a bright yellow fluid coursed along a transparent tube which wound through the apparatus. “Two.” Crackling electrostatic energy flashed blue, buzzing the copper coils. The needles on a dozen dials and pressure gauges span and flicked.

Harriet concentrated on the dial Annabel had asked her to watch. The needle seemed like an exclamation mark; a warning sign, blood red.

“Three. Now!”

Harriet squeezed.

A thick green fluid oozed up through a glass tube, dribbling into a conical flask. At the same moment the yellow substance shot through the last section of tubing and squirted in a spray, mixing with the green stuff.

Harriet was about to ask if she should stop squeezing when a green flame seared the air, leaving a blackened mark on the ceiling. Pipes and tubes rattled and clattered as if in an earthquake. Dials span. Shrill jets of steam shot out in all directions. And the flask exploded.

Harriet only realized she’d been knocked off her feet when she landed hard against the wall and slumped back down on the floor. Greenish slime covered her. Wiping the goo from her eyes and mouth she pulled herself back to her feet.

“Annie?” she said. Yellow smoke cleared. Annabel knelt amid the remains of the apparatus. She was scooping up a black globule about the size of a baby’s fist, into a petri dish.

“Got it!” she said, securing the lid.

“I thought you said that wouldn’t explode,” Harriet said.

“Shouldn’t have. Sorry,” Annabel said. “Look!”

Harriet picked her way through the debris to the scientosophical workbench where Annabel was busy adjusting a series of lenses, fixed in brass housings above a black box. She slipped the petri dish inside the box and peered into an eyepiece connected to it.

Annabel let out a low whistle. Then she stepped back from the eyepiece and invited Harriet to look.

In the narrow circle of vision, Harriet saw a magnified version of the black globule. But at that scale she saw it wasn’t a globule. It was a mass of things. Black, yes, but with thousands of tiny hairs and what appeared to be a dozen legs each. At least they didn’t seem to have teeth.

“Yuck,” Harriet said. “So is that what’s causing the plague?”

Before Annabel could answer there was a crashing sound from along the corridor beyond the laboratory. Someone shouted, raging. Harriet’s brow knotted. Her gut lurched. The disease could cause fits of violent madness in the final stages.

“That’s not Davy,” Annabel said, resting her hand on Harriet’s arm. The voice had died. Heavy footsteps thumped along the corridor.

“Then who…?”

The door flung open, crashing against the wall as a hulking figure stepped into the room, long hair tied back roughly and a savage beard sprawling over his chest. His clothes had once been fine, but his eyes were wild, bloodshot and glazed.

“Harriet!” he roared. “Where’s Harriet?”

Harriet stood up straight. Annabel’s hand slipped into hers and closed around it. The man looked at them both, eyes flashing between them. He spoke again, controlling his breathing, calmer.

“Please,” he said. “Which one of you be Harriet?”