Some said the Green Doctor’s roots grew so deep, if they ever left the leaning tower, the tower would fall. In truth, nobody knew how deep their roots went.

Eolh and Laykis came in through the underway. Though this path was drier than most, climbing through sewer pipes was not something Eolh liked to do. Give me the open skies over this dark, disgusting drainpipe.

The air was ripe with the smell of decomposing vegetation, and in some places, Eolh could make out the bricks and debris of half-buried buildings from long ago. Brown, brackish water trickled down the center of the pipe, making the stones slippery beneath his talons.

But at least there were never any guards down here. Only the bones of a few unfortunate vermin. And some larger bones too. Piles of dirt, glistening with moisture, were pushed against the curved stone walls, and stiff, muddy roots reached down through the cracks in the stonework. Some belonged to trees, some to the Doctor.

Eolh beckoned Laykis over to a set of handholds and missing bricks in the stonework, the closest thing this place had to a ladder. It had been well used back when the resistance needed a way to travel hidden from imperial eyes.

“Corvani,” the android said, “how much do you trust this Doctor?”

“They’re good enough, for the right price.”

“They?”

“Yes. They.”

“Then where did they study?” Laykis asked. “Where did they attain their medical license?”

“License?” Eolh cocked his head.

“Oh,” Laykis said, wrapping her arms more tightly around the human. “I see.”

“Look, we don’t exactly have a lot of options right now. Just let me take the lead. And be ready.”

“Ready for what?”

“Just be ready.”

Eolh hoisted himself up the ladder and pushed hard against the iron grate that separated the sewers from the tower’s lowest levels. A slash of light poured down into the sewer, and the sweltering heat came soon after.

The basement of the leaning tower was lit up, bright as day. Dozens of heat lamps hung from the wooden ceiling, shedding their hot, orange light on every corner of the room. Wooden struts held up the sagging ceiling. The struts were so overgrown with roots they almost looked like trees.

Wires and plant tendrils stretched across the ceilings and the floors, some of them wrapped around each other, some submerged in pools of standing water. All of them disappeared into the ramshackle maze of the basement. Cabinets and cupboards and baskets lined the walls, each one filled with bones or lined with vials and powders and herbs. Wrist-sized roots grew down into the floor, splitting open the foundations even further. And where the lamps shed their light, dark green leaves grew in thick clusters. The air was so hot and humid it was like trying to breathe in steam.

This was why Eolh avoided seeing the Doctor. This and the fact that the Doctor wasn’t exactly thrilled with Eolh’s debts.

Fortunately, Eolh had an idea.

Eolh motioned for the android to follow. “Don’t step on the leaves,” he said, pointing at the budding pods that were only just beginning to unfurl on those gnarled limbs. They went into a hall, where the roots on the floor and the walls joined together, growing wider and thicker until they dipped back below the floorboards or disappeared up into the ceiling.

Eolh brought them to a trunk so vast it had swallowed the stone wall it was growing out of. Its bark was hard and gnarled with age, and there were deep, dark gaps in the wood which were so spacious Eolh could almost climb inside.

Eolh knocked on the bark.

A vine descended from the ceiling. One great yellow eye hung on the end of the vine—its veins as green as a sapling—and when it saw Eolh, it blinked sideways. A single vertical pupil stared back, surrounded by an iris as emerald as the forest sunlight.

“Doctor.” Eolh bowed slyly, hoping his charm would help him carry the conversation.

A scratchy, whispery voice filled the room. “You . . . are not welcome here . . . Eolh of Crowcaste . . .”

The voice was a hot wind pumped through a hollow stump. It seemed to come from the trunk and from the gaps of the thickest roots, groaning and ponderous.

“Look, if this is about last time—”

“No . . .” It spoke slowly, a gust of wind between every phrase. “This is about every time . . . every time you come to me . . . you have some excuse . . . to escape my payment.”

“This time is different.”

“The Cauldron is in lockdown . . . the imperials march . . . and my tower feels strange . . . but you are still . . . an unwelcome thief.”

With a wet squelching sound, the stalk started to retreat back into the ceiling.

“Wait!”

“Leave my premises . . .” The voice whistled from the trunk growing over the stone wall. “I will summon . . . the authorities.”

“No, you won’t.”

“Oh . . . ?” The eyestalk stopped. Blinked. “And why . . . is that?”

Eolh beckoned the android forward with a gentle flap of his wing.

“I am no tinker . . .” the Doctor said. “I do not heal constructs . . .”

“Show them,” Eolh said.

Laykis peeled the cloak away from the human’s face. He looked worse than before. Deep, dark creases underlined his closed eyes, and his lips were cracked and dry, the skin turning ashen white. The wound carved a black line through his short, curled hair.

“What . . .” the voice from the trunk said. “What species is this?” The eyestalk stretched forward, the rays of its pupil swelling and refocusing with each blink.

“This is a human being,” Laykis said. “The very last one.”

“Oh . . . oh!” The trunk groaned in a language that Eolh had heard before but did not understand. “Achin . . . woan . . . ?”

Then, the eyestalk whipped around and thrust toward Eolh’s face. “Crowcaste! What have you . . . done . . . ?”

But it was Laykis who intervened. She lifted the human child toward the trunk and spoke with a great need clicking in her voice. “Please, Healer. Can you help him?”

A wind rushed out of their trunk, a humming, harmonic sound. One long vine wriggled up from the floor, slowly winding its way toward the human’s face. Another dropped from the ceiling. When the vines touched the human’s skin, they recoiled.

“It’s . . . hot,” the Doctor said. “Should it be . . . so hot . . . ?”

“You’re the doctor,” Eolh said.

“Never seen . . . one of these. The last . . . gone long before . . . my germination. But, perhaps . . .” Vines began to emerge from gaps in the wall. Their tips were sharp as thorns, made to slice open flesh.

Eolh slapped the vines away, and Laykis pulled the human back, cradling it in her arms, shielding it with her body. It had stopped shivering, which probably wasn’t a good sign.

“No surgery,” Eolh warned. “This isn’t one of your experiments, Doctor.”

“How to help . . . this creature . . . if I can’t . . . open it . . . ?”

Eolh raised his eyebrows knowingly.

The eyestalk shook back and forth. “No . . . Crowcaste . . .” It came as a scratchy whisper, more like the breath of a bellows than a word. “Absolutely . . . not . . .”

“It’s the only way.”

The Doctor was an ancient being. Some said they were older than the Cauldron itself. Eolh didn’t know if he believed that. But he did believe the rumors about the Doctor’s supply of nanite. An ancient human healing technology said to cure any disease.

Incredible stuff. Incredible—and rare. What one poor soul could buy with a single tube . . .

All the Doctor’s vines began to retreat into the walls and the floors and the ceilings. Eolh grabbed the eyestalk before it could escape.

“Remove . . . your appendage . . . Crowcaste. The nanite . . . is not for sale . . .”

“Good, because I’m not paying for it. I’m a thief, remember? Isn’t that what you called me?”

The eyestalk wriggled in his grip, and Eolh whipped out his blade, holding it an inch from the eyestalk’s pupil. Forcing the doctor to focus on the jagged edge of Eolh’s knife.

“You know I don’t want to hurt you, Doctor.”

The Doctor hissed like a dozen gas bladders filling up all at once.

From somewhere across the room, Eolh heard the scuffing of footsteps on the stairs leading down into the basement. One of the Doctor’s attendees, a small amphibious thing with a fat, colorful tail, had come down to investigate. Its eyes bulged with fear, its sticky hands clasped to its chest.

“Get back upstairs!” Eolh said without taking his eyes from the Doctor’s stalk. It squeaked and retreated with the scampering slap of wet footsteps.

“You know what this means . . . don’t you . . . Crowcaste? You will never repay . . . this debt . . .”

“The nanite, Doctor. Come on. We don’t have all day.”

Numerous vines crawled back up the walls, disappearing into the dark pockets and cracks of the foundation. Then they came back, snaking down the ceiling. One was wrapped gently around a glass-and-metal tube as long as Eolh’s hand and as thin as his finger. There was a red symbol on the white metal and tiny black writing along the side.

“How do I know you haven’t opened it?” Eolh asked, still holding the knife tip to the eye. “How do I know that’s real nanite?”

“It is real,” Laykis said.

How would she know? Eolh wondered. But she was looking at it with a kind of reverent intensity, and before Eolh could say anything, she reached out and grabbed the tube. In a single motion, Laykis clicked open the tube, though Eolh couldn’t quite see how. She pulled the human’s lips apart with those smooth, silvery fingers of hers and started to pour.

“A drop!” the voice from the trunk whispered. “He should need . . . only . . . a drop!”

Laykis ignored him, tipping all the silvery, metallic liquid into the human’s mouth. She smeared it into the wound on his scalp too.

The trunk sighed. “Do you have any idea . . . how expensive . . . that was . . . ?”

Laykis shot a glance at the great yellow eye. Despite the smooth, featureless mask of her face, even Eolh could feel the righteous fury boiling inside the android.

The Doctor was quiet.

Silvery strands, almost invisible to the naked eye, began to stitch themselves over the human’s gouged forehead. But the human did not move.

They waited. Eolh slackened his grip on the Doctor’s eyestalk, and the eye immediately moved out of his reach. But nobody left. All of them watched the human as Laykis wiped the dribble of nanite fluid off the human’s chin and smeared it over his lips.

“What if he’s already lost?” Eolh asked.

The human coughed. He rolled slightly in Laykis’s arms, unconsciously adjusting his position. He did not wake, but there was movement beneath his thin, dark eyelids.

“I . . . hear something . . .” the Doctor said.

Eolh listened. Heard nothing.

“Imperials . . . they’re . . . coming . . .”

“You’re just trying to get us out of here.”

“No . . .”

“Then why would you tell us that? Why would you help us?”

“You can’t pay me back . . . thief . . . if you’re dead . . .”

“Ah,” Eolh said as understanding dawned. “Thanks for that, then. Guess I owe you one.”

“You owe me . . . many . . .”

“Which way are they coming from? Where should we go?”

“Above . . . the ground and . . . the tower . . .”

They were surrounded, and every way out was being watched. Even if Eolh could somehow fly the human out, every gang’s safehouse would already be closed. Nobody wanted to get raided, and the Empire loved their raids.

There was only one obvious answer.

“Where else . . . can you go . . . ?” The Doctor’s eye stared at him, expectantly.

“No,” Eolh groaned, dropping his head into his hands.

“Yes . . .” the Doctor breathed. “The underway . . . is not done with you . . . yet.”