Here's my specific example:
Puffing, Ralphie rested her elbows on the guardrail. Body Woman was now talking to a bald super spy.
(For context, Ralphie is on a balcony looking at Body Woman and the super spy.)
Is this grammatically correct for what is supposed to be a third person past tense narrative, or does it ruin it by bringing in the first tense? I don't want any 'it depends on the writer' nonsense. Just yes or no answers backed with arguments please. Also, if it is not grammatically correct, what should I replace 'now' with in a sentence like this in order to get the point across that there has been a change in the situation and now something is happening which was not happening before? The best answer gets a prize.