(Dear god please tell me you didn't just bring Cyber-fish-people into the story. Oh my god I love you. And I've been meaning to post but I've been sick all week and home from school plus we had my grandma's funeral last night/this morning. So hey. You know.)
As they reached the shore, the water pulled the sand away from around the Doctor's shoes, his feet sinking into the wet ground beneath his feet just so slightly as he stepped away from the crystal water. He smiled. "I guess I did win!" He almost jumped in excitement-the Doctor loved a good race, you could tell if you'd seen him on a daily basis-but then he saw the metallic creature. Instinctively, he put a protective arm around Mercy, his eyes narrowing into a scowl with a hint of fear in them.
"Mercy?" He paused for a moment. "That may or may not be one of the most dangerous creatures known to...well, anyone who knows about them. I'm not sure...but I do believe that's a Cyberman." He breathed deeply. It didn't look hostile, but then again, it didn't exactly have a way to change its facial expressions either. But if it was hostile, surely it would have attacked by now...perhaps the water had forced it to malfunction. And it appeared to be fine around the Ergen natives...maybe it wasn't a Cyberman, but perhaps a simply silver fish-person...but when he heard, very quietly, the words, "The Doctor will be D-E-L-E-T-E-D" as it stepped closer, he realized that it was exactly what he had feared.
"They just keep coming back, don't they...And I thought I got rid of you. I thought when I lost Rose that was the end of these miserable, emotionless shells. But no. Just like the Daleks, you keep coming back, don't you?" He almost spat the words at the metallic alien, still pulling Mercy close to him in a protective embrace. He wouldn't step back, but he had to know whether this thing was dangerous to them or not. It had said 'DELETED'...but perhaps its software was contaminated by seawater. And then it stepped closer. Slowly, deliberately, and the Doctor's face showed fear this time, because he knew he couldn't run. There was nowhere to run-and if he ran people would be hurt or killed. Where there was one Cyberman there would be many more, he knew, and this thing couldn't have survived alone. They were trapped now...there was only the Cyberman and water...death or..."Oh, BRILLIANT!" He cried. "Mercy. Step into the water. Now."