This story is part of the My Unsung Heroes series from the Hidden Brains team. It tells the story of someone whose kindness left a lasting impression on others.

More than 20 years ago, Virginia Squier accompanied a group of middle school students on a tour of England. She brought her daughter, Chambers, who was 8 years old at the time.

One evening, towards the end of the visit, Squire, her daughter and the school group were on a platform on the London Underground, preparing to move on to their next destination. It was five o'clock in the afternoon and the station was packed with people. Squire took Chambers' hand and began counting her students. Just then, a train stopped on the platform.

"All of a sudden, my daughter let go of my hand and jumped on the train and the doors started closing," Squire said. "As the train accelerated, I ran to the side and tried to force the door open by inserting my fingers into the black rubber gasket. On the other side of the glass, I could see my daughter's panicked face."

The last thing she saw before the train pulled out of the station was Chambers crying and banging his little fists on the glass. Behind her, a young man wearing black leather and a spiked dog collar around his neck stood up from his seat and started walking toward Chambers.

Squire became frightened and began looking for an employee. The person she found was not a native English speaker, which made explaining her situation difficult.

"I was too shocked to cry when one of my students suddenly appeared on my shoulder, I was too focused on getting this person to understand my plea for help," Squire said. "'She's back,' she said. I turned around and there she was... my little girl."

The man on the train witnessed what was happening and came to help. He comforted Chambers and guided her off the train at the next stop. They then boarded another train to return to her mother.

"My preconceived notion that he was scary was shattered," Squire said. "I remember looking up at him and breaking down crying, hugging my crying baby. When I looked up again to thank him, he was gone."

Weeks after the incident, Squire would break down in tears just thinking about how the situation could have turned out differently. She hopes to find her unsung hero and express the difference he made.

Chambers told Squier she believed the man was from the United States, possibly Indiana or Minnesota.

"So I fantasized about putting an ad in the newspaper or putting up a billboard on the highway so I could find him and thank him," Squire said.

Squier said the man didn't just save her daughter. He changes the way Squire lives in the world and teaches her to be a more accepting person.

"To this day, when I find myself judging someone based on their appearance, I still have that image of him in my head. I want him to know that he saved me from the worst day of my life."

My Unsung Hero Is Also a Podcast - New episodes released every Tuesday. To share your unsung hero story with the Hidden Brain team, record a voice memo on your phone and send it to myunsunghero@hiddenbrain.org.