He was terrified - that was the truth of it. Bad Wolf could only mean bad - the end of the universe.
"What is it?" Donna asked, terrified. The Doctor suddenly turned on Donna, walking quickly towards her.
"Who was the woman?" he asked Donna. "Who was she, what was her name, what did she look like, where did she say she was from?"
"I can't really remember, she never told me her name. Every time I asked... she'd never say. But she told me where she came from... I can't remember. But she was nice, she was kind, she helped me!"
"Donna, what did she look like?" The Doctor pressed. "Did she have blond hair?"
"Yeah, she did. And every time I saw her, there was like this flash of light, and she'd appear."
"Donna," the Doctor stuttered, "Did... Did she look like this?" He grabbed a creased photograph out of his pocket, holding it in front of her face. His hand shook.
"Yeah, she did a bit. Who is she?"
"That... That is Rose." he replied slowly, placing the creased photograph in his pocket. Donna stared confusedly at the Doctor.
"But you said... You said she was lost."
"The last time we were together she... she was trapped in a parallel universe. It's not poss - she can't be back here, she can't. There was no way through, I searched, I searched. Every day, Donna, I searched for a small gap, a tiny glimpse of hope. She can't be back, Donna, she can't."
"Well, she was," Donna replied quietly. She then spoke louder, "Now, are you going to keep arguing about how she can't be back, or are we going to go back, see your Rose again and save the universe?" The slowly-forming grin on his face answered her question.