The floor of the sea was terribly uneven. The Doctor had thought they were heading upwards, back towards the lagoon, when it became clear by the heavier presence in his lungs and on his skin that they were, in fact, deeper than before. Even though he couldn't breathe as quickly, he found himself more alert. It seemed the thicker nature of it also increased its oxygen density.

The Doctor slowed to a stop. Of course! That explained why people drowned in the Dregs. If they managed to survive the air-to-sludge transition, most probably went on instinct and either tried to reach the surface or stayed as high as they could within the layer of muck. The higher you are within it, the less concentration of oxygen, the faster one has to breathe, and--

There was a light touch on his arm. The Doctor turned to see Rose looking at him with concern. He gave her a reassuring smile and started off again, deciding he and Rose stood a better chance down here than where they had been.

Until, that was, the bulk of a giant shell powered right past his face. The Doctor pulled back in shock, wide eyes following the mass of writhing tentacles as it retreated into the hazy pink distance. He took a few moments to just watch and listen. This time, Rose's touch on his arm was in the form of a death grip. He looked to her and brought a hand up to her face. She was terrified.

'What was that?!'

'A local, apparently. It doesn't seem as interested in us as the crocodiles were, so let's keep moving. Okay?'

Rose took a deep sludgy breath and nodded.

'Yeah, I'm okay. I've got you.'

The Doctor offered his warmest of smiles and she released her grip from his arm to squeeze his hand. He wished he could hold hers as they went, but it made swimming difficult. There had been a good reason he hadn't regenerated aquatic after all.

They hadn't progressed far before they had seen another of the creatures, and then another. The shelled beasts were very similar to the nautilus of Earth, the Doctor noted. Every time one passed them, they stopped to watch what it would do, and each time, it would leave them alone.

The creatures did notice them, however. One would approach and hesitate, as if trying to make out what they were, before carrying on.

It was just after the Doctor and Rose had come across two at once that they encountered the mother of all nautili. He doubted even ancient Earth had any so large. It was so vast, the Doctor didn't recognise it for what it was, at first. The muck was all motion, a writhing sea of movement and currents associated with so many giant tentacles roping through it. Its great head was faded in the distant haze, the rim of its massive shell on the edge of visibility. Absolutely beautiful!

One of those huge tentacles suddenly began snaking towards them.

The Doctor yelled uselessly in warning, attempting to brace himself for the impact of it. It had reached them in seconds, but instead of hitting hard, it gently curled around the Doctor's middle, thick like an elephant's trunk, but smooth, no suckers. He craned his neck, desperate to see if Rose was all right, and to his surprise, it had so far left her completely alone.

'WHY DO YOU COME HERE?'

The Doctor was taken aback. He stilled, staring at its center.

'Oh... hello. Um, I'm the Doctor, and this is Rose.'

He gestured to the terrified girl, who was shaking slightly in her dark bikini and watching him, looking entirely without a clue as to what to do. The Doctor fixed his eyes back on the distant head and projected firm thoughts of warning.

'Don't you touch her.'

The nautilus seemed to not have heard this. Instead, the Doctor sensed its change of perspective, the band of muscle wound round him loosening ever so slightly.

'DOCTOR...? CAN YOU... HELP ME?'

He frowned. What?

'...Sorry?'

'HELP ME, DOCTOR. I AM THE BROODMOTHER. HELP MY CHILDREN.'

The Doctor could tell by the way she imagined them that they were much too young to be the 'children' swimming about her that needed the help she sought. Directly, anyway.

Could he help? Possibly. Did he want to?

'How do I know you won't just eat us once I've helped you?'

There was a pause as the Broodmother thought.

'I SMELL BLOOD. ARE YOU INJURED?'

'Oh, I'll say we are. Your croc cronies were none too gentle getting us down here. They are yours, aren't they?'

'I WILL TRY TO HEAL YOU. TRUST IN ME.'

The Doctor didn't see they had much choice in the matter, seeing as the tentacle hugging him put an anaconda to shame. He did notice, however, that she was politely waiting for his consent. The Broodmother needed his cooperation, after all, and therefore wanted to show her respect for that need. Clever, this one.

'Get on with it, then.'

The response was immediate, the living rope tugging him closer, away from Rose.

'Wait! She comes with me!'

Another tentacle lashed outwards, and in seconds, Rose had been caught up in it.

Rose didn't seem to like it one bit. The Doctor was instantly resistant. None of this was worth her fear.

'SHE'S FIGHTING ME.'

'She doesn't know your intentions!'

'HER MIND IS NOT OPEN.'