Dean stepped into the tower. The darkness closed behind him, and for the first time in two days his eyes were unable to see. The cool, damp, darkness was like a wet towel on his face. A tension he hadn't noticed growing around his eyes began to fade.

"Are you ok?" said Emma from outside.

"Fine" he took one more step inside. The floor beneath his feet felt hard. He guessed it was bare concrete. There was no trace of dust or rocks. His eyes began to adjust to the darkness. The gloom seemed to be thinner at eye level and he thought he could see a current: eddies in the dark. It was flowing towards the open door, spilling out to pool at the base of the tower. Looking down, his body was still lost in the darkness, but he began to make out the fuzzy gray outline of walls and objects.

"I think it might get less dark as we ascend." he said, "I'm going to look for a way up."

He shuffled across the floor, his hands out in front of him, until he reached a wall. It was cool and rough and slightly damp. He kept one hand on the wall and followed it around until he found an opening. Kicking out with his foot, he found a step. "I'm going up."

"Wait!" Emma's voice was faint through the darkness. "I'll come with you."

He heard her muffled footsteps enter the room. "Over here" he said, and he slapped the wall to give her a sound to follow. She bumped into him and felt blindly down his arm until she found his hand, she held it tight. Her hand was warm and moist with sweat. It felt too real nestled there in Dean’s, the rest of the world fading to dreamlike transparency. His heart thumped loudly in his ears. He tried to concentrate, feeling his way up the stairs, one step at a time, using his foot to make sure the next step was there before shifting his weight. One hand on the wall, the other linking him to Emma. He counted 17 steps before the floor levelled off. The darkness was thinner here, he could see the outline of the room clearly down to his feet. Four walls, a table, the staircase. The slits in the wall were visible as lines of grey in the black. The currents in the blackness were clear now: it billowed down the stairs from the floor above, spreading out into the room, then flowed down the stairs they had just come up. It was coming from above them. They went up another story, and another, and another. Each floor was the same: an empty concrete room, little more than a landing, most empty of furniture. A door separated each room from the stairwell above, but all were propped open. The darkness continued to fade as they rose, the river of blackness that flowed down the stairs becoming more defined. By the ninth floor, they were almost in full light. The blackness was a thick, tight, tendril, a stream of sticky, weightless, oil that flooded down the stairs. They climbed up through that river of murk, their feet heavy and dragging in the blackness, though Dean thought it might be his imagination, and emerged into the light.

The tenth floor was the top of the tower. On their left, a walkway extended outward, going six or seven feet before ending abruptly in a mess of twisted metal and dropping 100 feet above the rocky ground. Dean could see a thin layer of murk at the bottom of the tower where the darkness flowed out the door. On one wall, a large opening looked out over the wastelands, facing back the way they had come. Emma dropped Dean's hand and ran to stand at the window. "Look, I can see the classroom!" she said, pointing out at a speck of red stone in the distance. She stared out at the view. "There doesn't seem to be anything else that way." she said, "Just grey rock." She leaned further out the window, peering around the corner to look in other directions.

"Don't lean." said Dean, "I'm not good with heights..." he wiped his sweaty hand on his trousers.

"It's fine!" she said, "I'm not going to fall, don't worry."

"God, just..be careful. I can't watch." said Dean. He turned to look at the other side of the room, the tendril of blackness snaked up the stairs and flowed through an empty doorway, filling the room behind. Was this the source of the dark? Might there be something in there they could take with them, to banish the eternal day, to get some proper sleep? He approached, then stopped when he saw a vending machine, tucked behind a pillar next to the doorway. The door was lit. The light flickered on and off, shining through the glass door, revealing the rows of chocolates and crisps behind. It was almost full. He felt a sharp ache in his jaw as his saliva glands reacted. "Emma, you have to come see this. This place definitely came from earth. They have Mars bars and everything."

"Hold on, I'm trying to see what's in the other direction."

Dean looked back and felt nausea rise in his stomach when he saw what Emma was doing. She had crawled out along the ruined walkway and was now lying down and peering over the drop, trying to see out in the opposite direction to the ruins.

"What are you doing?" he hissed, "it's not stable."

"It's fine", she called back cheerfully, "it doesn't even wobble. I just need to edge out a bit more to see what's — oh..."

"What?" Dean edged nearer to the walkway. Even ten feet away he felt dizzy at the drop, sure that he would trip and fall any second, plunging over the edge and hurtling toward the stony ground. I could trip and fall flat on my face, and still be a few feet from the edge he told himself, but the fear didn't listen.

"I can see water, on the horizon!"

"Are you sure it's not just heat haze?"

"No, it's definitely water, I can see it moving, It looks like a sea. The whole horizon is covered! It's beautiful. Sparkling and blue. There are waves! Come see!"

"No...I'm fine here. Why don't you crawl back over this way, first."

Emma looked over her shoulder and smiled naughtily. "Am I making you nervous, Dean?" She sat back onto her knees and then pushed herself to her feet, standing only one pace from the edge, then she spun around and swaggered back down the walkway, laughing at Dean's pale face. "Don't pass out" she said, "I didn't know you were so scared of heights."

"Yes...just a bit."

He grabbed her arm as soon as she was in reach, and she laughed again, her face was flushed from the excitement. "You worry so! I didn't know you cared that much!"

"Ok, god. Calm down, I'll have a heart attack." said Dean, "come look at this vending machine, way over here, far from the dangerous drop."

"Vending machine?"

"I swear." he dragged her over and they both stood in front of the thing, the buzzing light reflecting on their faces. They stared at the machine for a moment, eyes fixed on it, moths drawn to light.

"Well this makes our trip worth it, even without finding the sea." said Emma, "the others are going to love us when we come back with armfuls of chocolate."

"It's going to be a welcome change after puckleplum, yeah."

"Do you have a coin?" said Emma

"No...I imagine we might have to break the glass."

"Wait, how come it's still running? There can't be any electricity in here. Is it battery powered or something?"

"Maybe solar panels?" said Dean. "If so, that's more exciting than the food. Imagine what we could do with electricity."

"I guess. I'm more into the chocolate, right now." Emma reached out one finger toward the keypad. Dean was looking behind the machine now, trying to find a cable where it was getting its power. He crouched. A thin black tendril was attached to the machine, emerging from a gap in the case and following the wall around into the dark doorway the river of darkness seemed to be emerging from. It pulsed rhythmically.

"Trix, hold up. I think something's not quite—"

The moment Trix's finger pressed down the 'A' key, blackness erupted from the doorway. It pushed Dean off his feet even as it obscured his vision. It filled the room, billowing out in all directions, bursting out through the window and the walkway. He heard Emma's muffled scream and clambered in her direction, she kicked out at him and he yelped "It's me! it's me", he grabbed her hand and they both crawled toward where they remembered the stairwell to be. Behind them, something was moving through the room with a noise like sucking mud.