An old friend used to give writer conference talks, and she would open with a story about a quite famous piece she'd written, dealing with AIDS in rural US.
Her conference talks, summed up:
She'd arrived at the hospital bed of a subject, covered in tubes and machines and clearly dying. his family was deep in talks about whether the time to end life support was now. The discussion was heated and laden with guilt (many had abandoned him on learning he was gay). Finally, a family member turned to my friend and said, "You spent more time talking to him, and about life and death topics, than any of us." the other family soon chimed in and agreed, she was the only person who really knew what he would have wanted. the decision on whether or not to end life support should be his, and as she knew better than they, would have to be hers. She realized the next words out of her mouth would determine whether this young man died today, or lived.
And that's where she stopped her story and started talking about writerly stuff, etc.
That, to me, is the essence of what we want in our first 700 words. It doesn't need to explode, unless it needs to explode. But it needs to grab a reader and make them shout "WTF happens next?"
It's Hitchcock's bomb on the bus, Show the reader the bomb. Make it clear that the bomb is going to explode. But you can't detonate that bomb. then you detonate that bomb.