A possible concise summary is:
- The text contains four stories of school lockdowns from different perspectives and situations.
- The first story is about a substitute teacher who let in a man with a gun who was looking for his ex-wife, another teacher.
- The second story is about a college student who encountered a suspicious man outside her dorm who claimed to have a gun and followed her to her window.
- The third story is about a fourth-grader who left the classroom during a lockdown and met an armed intruder who was screaming anti-Christian insults.
- The fourth story is about a high school musician who heard a man banging on the door and chanting Islamic phrases.
Here are some possible facts extracted from the text:
1. The text is a collection of stories about lockdowns in schools.
2. The first story is about a substitute teacher who let in an armed man who was looking for his ex-wife, a math teacher.
3. The second story is about a college student who encountered a suspicious man who claimed to have a gun and followed her to her dorm building.
4. The third story is about a second grader who left the classroom during a lockdown and saw a man with a gun in the hallway.
5. The fourth story is about a fourth grader who witnessed a man banging on the door and shouting anti-Christian insults during a lockdown.