The corridor spat them out in a vast, impossible chamber.
It took a few seconds for Charlie's brain to process exactly what he was seeing – and even then, he couldn't make head nor tail of it.
They were inside a strange, MC Escher-sque palace; white marble staircases criss-crossing impossible dimensions, linking paths which couldn't conceivably be joined.
Trying to follow a straight line which somehow converged back on itself was making his eyes water, so Charlie turned to the Doctor, who was muttering thoughtfully to himself, his sharp gaze peering at the scene around them through his furrowed brows.
"…Castrovalva…" the Doctor murmured.
"I'm sorry?"
"A trap… the end… or merely the beginning…?" the Doctor continued in an ominous whisper, "For whom does the Cloister bell toll?"
"Are you okay?" Charlie enquired, tapping his elbow.
"What…?" the Doctor glared at him, a puzzled expression rippling across his aged features. "Yes?"
"Which way do we go?" asked Charlie, examining all the exits, archways twisting in all directions.
"I can't tell. This reality doesn't make sense."
"Reality's just an illusion?" Charlie recalled.
"Yes," the Doctor murmured thoughtfully, "You know, that's a very interesting perception."
Charlie frowned. "You told me that. Well, a weird shadow version of you did."
"A weird shadow version of me?" the Doctor queried, raising an eyebrow, "You don't mean the antibodies?"
"Uh… antibodies?" Charlie wasn't entirely sure what the Doctor was suggesting.
"Yes. They hunt down foreign objects – much like yourself. They get everywhere when I start regenerating," the Doctor rubbed his chin, "Sometimes they manifest themselves in my head as ghosts of my former lives." The Doctor shook his head disapprovingly. "It's very distracting. What is odd though, is that they don't speak."
A jolt of realisation hit him like a bolt of lightning. "You mean…?"
"Whoever told you that… it wasn't me. It wasn't from my head."
The Doctor was glaring at him. Charlie immediately felt pressured into a response under the intensity of the Doctor's piercing gaze.
"You mean… there's something else in here? Something else in your mind, aside from us?"
"Yes." The Doctor continued to stare at him, as though he were expecting him to say more.
"It wants to kill us," Charlie warned, "It wants to kill you."
"I know." The Doctor shrugged, and turned away. "You don't happen to know what it is, do you?"
"No," Charlie admitted, "Do you?"
"No."
The Doctor ran his fingers along the rough stone wall of the TARDIS, struggling to get his bearings.
He began to hum, which Charlie found somewhat jarring, but also strangely reassuring.
"Don't get lost inside your head…"
The Doctor frowned, and turned his owl-glare to Charlie. "Hmm. At least my subconscious still has a sense of humour."
Charlie bit his lip, and slid his hands into his trouser pockets – standing there quite awkwardly as the Doctor stared at him, unblinking, for an uncomfortable length of time.
"Um, Doctor?"
"Shh! Listening!" the Doctor hissed.
Charlie nodded, and automatically shut up.
"The way forward is just out of reach…" The Doctor whirled round, his gaze darting in all directions at the twisting roads bending all around them. He made a strange throaty growl as he whirled around.
"Oh, no! No, it's up there," he uttered brightly, pointing in a seemingly random direction – towards one of the many, impossible staircases.
Charlie followed the Doctor's gesture. "You can tell?"
"Yes, can't you hear the path?"
"I… what?"
Charlie peered at the Doctor, then back up at the misshapen archway the Doctor was pointing to.
Now he had grown accustomed to this strange world, he could hear something. It sounded like… a river? A trickling of water, splashing against rock and metal.
He began to see the droplets falling from the hairline strand of black oil, arcing across the space, each following a strange parabola which blossomed from their destination.
"You can hear the river's song?" the Doctor grinned.
"Yeah!" Charlie breathed.
"Come on!"
He followed the Doctor, across those impossible Escher-esque paths. He did not enjoy the sensation of following one staircase and crossing gravity-defying boundaries into the next.
Still, they made it, breaching one last dizzying change in direction.
And there, just ahead of them, another of the Doctor's TARDIS.
The Doctor shot a glance at him – and they both knew what this meant now. They were about to enter another layer of consciousness.
"Stay close," the Doctor urged.
They followed the river inside. Charlie expected to see another version of the TARDIS console, but this time, it was nothing like that.
They had stepped into a giant watch, or perhaps a clocktower. Grinding gears and cogs - twice as tall as a man – rumbled as they twisted through the walls, scything the space into fragments. Charlie couldn't tell what the mechanisms were made of – if they were made of anything at all.
Now that he thought of it, he wasn't sure what he and the Doctor were made of. They were vague shapes, memories of humanoid forms.
Deep tolling bells hammered at his brain, erasing his thoughts. The only thing Charlie could be certain of, was that they were very much here. They were deeper inside the Doctor's consciousness, past memories, past subconscious thought. They were now in the foundations of his mind.
"It's coming for us," the Doctor growled, casting a glance over his shoulder.
"What is?"
"The slowing of your heartbeat. Death."
Their path twisted through the spinning gears; Charlie trusted the Doctor's timing as they jumped through swinging spokes, and oscillating blades swiping the air as they passed.
The Doctor danced and leapt through this vast and vicious industrial hell. His grace among the grease and dirt was inspiring; Charlie's clumsy imitation of the Doctor's skill was almost getting him killed.
The sheer size of the clanking machinery, suspended by invisible axles, finally hit him in drunken realisation. They were tiny. The snarling teeth of the cogs would chew them up, crush his bones.
What the hell was he doing? Why the hell was he wandering blindly into deadly peril?
The Doctor grabbed Charlie's hand, redirecting his focus. They were fleeing, fighting.
But the Doctor was losing. He could feel it. The Doctor was losing his battle against death. With every breath, he was failing.
Charlie experienced the Doctor's torment as though it were his own. He could feel his one heart struggling to pump his thick, congealing blood through his veins. His ragged lungs inhaled flames. But most worryingly, he was losing control of his senses.
His hearing had faded first. The clanging cloister bells drowned in silence, only to be replaced with a deafening white noise; the last memory of sound. Then his sight of the world had dissipated into nothing, plunging them into darkness. He was acutely aware that he could be millimetres away from a death trap at any moment.
The only thing left was a faint sense of touch – the feel of the Doctors fingers, as he trailed behind him. It was the only thing left he could rely on to be sure he was running in the right direction. To be sure he was still running.
He had never felt so useless. So helplessly dependent upon another. He just prayed that the Doctor wouldn't give up now.
He was fighting for his life.
And there was no way Charlie would allow the Doctor to fight alone.
