This takes place directly after Detective Comics #411, which is Talia's introduction.
If you haven't read that comic, basically Talia and Bruce are both kidnapped by Dr. Darrk, a former associate of Ra's al Ghul (who is not actually introduced until a later comic). Talia removes an unconscious Bruce's mask to treat his wounds. Some more stuff happens, and it ends with Darrk trying to kill Batman with a knife, and Talia threatening him with a gun. Talia shoots him (possibly by accident? She looks surprised when it goes off) and he falls into the oncoming train.
Bruce was moving before he had processed what was happening.
The train was still speeding past, ripping Dr. Darrk to shreds as the gun fell from Talia's shaking hands. He reached her in record time, taking a moment to look over her wide eyes and trembling frame before she collapsed into his arms.
He pulled her in, a unique smell of flowers wafting from her hair as he turned her away from the spread of guts and gore that was Darrk's body.
After a moment of his fingers hovering over her hair, Talia began to regain her footing.
"Are you alright?" he asked softly, his hand landing on her shoulder.
She nodded, perhaps on instinct, before she tried to look around him. Bruce nudged her back gently.
"You don't need to see that."
"I am the one who killed him," she replied, only a slight tremor in her voice. "It is only right that I see what remains of him."
"The train seems to have done the worst of it."
She gave him a look. "I study medicine. I can handle something disturbing."
In silent acquisition, Bruce let go of her shoulders. Talia took a step over, her face deliberately blank as she took in the mess on the train tracks.
"That was the first time I have ever killed," she admitted, her voice soft.
Bruce was silent.
"Do you…" Talia hesitated. "Do you often kill, Batman?"
He shook his head. "Never."
She took a shaky breath, before turning back towards him. "We must hurry if we are to make the Express back to the city and the police."
"We can wait for the next one if you need time to collect yourself."
Talia shook her head. "I do not need to be patronized. We will go now."
Bruce nodded, before he hesitated, a possibility suddenly occurring to him. It could be a horrible idea, but… It might distract her from Darrk's death , he thought. Maybe make her feel more comfortable. "It might be better for me not to go on the Express in my Batman suit."
Talia tilted her head. "If you're not too uncomfortable." The lilt in her voice was almost teasing, and Bruce felt himself relax at the shift. "I seem to recall you feeling 'undressed' without it."
He ducked his head in embarrassment. "Well, you've already seen my face. And you're too clever not to recognize me the next time you see a picture."
"Is there something else to call you then? Besides the Batman?"
"Bruce," he offered, pulling off his cowl. "My name is Bruce Wayne."
"A pleasure to meet you, Bruce Wayne." Talia's smile could almost be considered sly, if not for the glimpse of sincerity underneath. "And have no fear. I will keep your secret."
He offered her a smile back. "Thank you, Talia."