If I'm understanding you correctly (sorry, I'm new at this) It sounds like you are describing an accident that either didn't actually happen, or was minor compared to what could have happened. I would call this a "near miss" or "close call"
Explanation:
For example: I had a near miss today when a dog ran out in front of me.
Or: He had a close call when his foot almost slipped over the edge of the cliff.
What is an important detail from the middle of the story?
It depends on what your reading, if in the middle of the story it talks about one character then its probably to give more info on them. So there for that character would be the main idea.