Tempus hadn't heard her. He had been too lost in his own mind to notice. At least, he hadn't noticed her until she spoke. The ageing Time Lord inhaled sharply, almost appearing to jump with fright. His hands clambered to keep a hold of the injector. He clutched it closer to his person, trying to conceal it from her. But perhaps it was too late for that... Still, she wouldn't have known what was inside. Would she?
Turning his head, he looked at her. Time flowed around her... well... normally. At least, as normally as they came. It looked strange around the people on the TARDIS. This was his River.
"Haven't you heard of knocking? It's a very simple thing. Humans tend to think they invented it for some reason but they think they invented chess, and I know the real story behind that" he said to her, his tone fairly flat. Like he was hiding something. "Why are you here, River?" he asked, standing up. As he did so, he attempted to palm the injector into his pocket subtly.