His uncle rushed the cockpit on 9/11. When bullets began flying at Annunciation, this Minneapolis dad knew what to do.

Devin O’Brien slipped into morning Mass a couple of minutes after it began. He sat next to his brother-in-law in back, his three kids in pews with classmates. Joy and excitement filled Annunciation Catholic School’s first student Mass of the new school year.

Some 400 people — students, teachers, older parishioners and a handful of parents — sang the opening hymn. It was about showing mercy to those in fear and casting hatred aside. They were about to stand and sing “Alleluia” when the first blasts rang out.

O’Brien immediately grasped what was happening: On the other side of the wall stood someone with an AR-15, intent on firing at these children in yet another horrific school shooting in America.

In his head, he heard a voice: Be a helper.

“I don’t know if it was God or Mr. Rogers,” O’Brien said later. “Maybe both.”

Bullets flew around him. Children hid beneath pews. O’Brien had to stop this.

And so the children and teachers saw O’Brien lead the charge, sprinting toward the danger — just like his uncle 24 years before, on the September morning that forever changed O’Brien’s life and the arc of American history.

Tom Burnett Jr. was O’Brien’s idol, equal parts funny and serious, someone who always challenged O’Brien to think deeply about life. Uncle and nephew were cut from the same cloth: Voracious readers, interested in history and debate and big ideas.

“There was a very specific code of manhood in my family,” said O’Brien‘s mother, Martha Burnett Pettee, one of Burnett’s two sisters. “You were well-read, honorable, religious, and you instilled values in your children.” As O’Brien’s brother-in-law, Shea McAdaragh, sums up O’Brien, “He believes in all the good parts of chivalry.”

Like his uncle, O’Brien craved adventure and had a keen ability to assess danger. “A friend told me, ‘If there’s an apocalypse, your son is going to be a survivor,’” his mother said. “It’s just in our DNA.” Even when he snowboarded off the roof and onto a trampoline at age 10, O’Brien’s mother never thought him reckless.

O’Brien admired how his uncle remained rooted in the family that formed him, even from California’s Bay Area, where Burnett lived with his wife and three daughters and worked as a business executive. Burnett called his parents daily. Burnett’s father — O’Brien’s grandfather — was the best man in his wedding. Burnett bought hunting property in Wisconsin where he’d hunt and fish with his father, and O’Brien joined the two on every outdoor adventure he could.

“I just wanted to crack into that, to be part of what they were doing,” O’Brien said.

The next morning, Burnett boarded United Flight 93.

Forty-nine minutes after takeoff came a voice on the intercom. “Please sit down,” the voice said. “We have a bomb on board.”

Four hijackers had commandeered the flight. From a seatback phone, Burnett called his wife. She told him about the World Trade Center. The family later learned from the cockpit voice recorder the heroism of Burnett and other passengers. They rushed the cockpit with improvised weapons.

“He said, ‘That’s our fate, so I better do something about it,’” Burnett’s sister said.

Back in Minnesota, O’Brien joined his family at his grandparents’ house, waiting, hoping, praying.

“I never was surprised my brother had the courage to do that,” Burnett’s sister said. “And I don’t have any surprise my son had the courage to run towards danger either. He’s spent his life saying: ‘What would Tom do?’”

Be a helper.

The words in O’Brien’s head were clear that morning at Annunciation.

He sprinted down the aisle, past where his fourth-grade son, uninjured, hid with classmates. He sped toward the east door near the altar, determined to stop the shooter.

“Devin ran towards the evil,” said Matt Stommes, a father of four Annunciation students, who was seated next to O’Brien in Mass. “His first instinct was to protect those around him.”

“I had a sense that death was inevitable,” O’Brien said later. “It was not that I believed I was going to be able to prevent this from happening. Because it was already happening. It was the absolute horror for the kids. I just remember feeling that the kids have to see that someone is willing to attempt to help them.”

He passed the principal, Matt DeBoer, who was running toward the outer wall where bullets were flying into the church. They locked eyes: We got this. That millisecond was profound, the sense that all the adults inside the church would defend and protect. Teachers shielded students; older students shielded younger students. O’Brien’s brother-in-law shouted at kids to get down.

O’Brien pushed the metal door to rush outside. The door didn’t budge. He wasn’t sure if it was locked from the inside or sealed from the outside by the shooter. He paused to think: Maybe instead of getting outside to stop the shooter, the better plan would be to ensure the shooter didn’t get inside.

O’Brien yelled to his brother-in-law and Stommes to guard the glass doors at the back of church. “We needed to survive for a couple minutes,” he said later.

He heard a thud outside: Something slamming against the door. (Later, a police officer told him it was the shooter throwing a jammed handgun at the church.) As bullets flew around him, he slammed shut a second set of oak interior doors. A foot in front of him, three bullets hit those doors. He pushed an injured student under the first row of pews.

“There are kids that need aid immediately,” O’Brien recalled thinking. “We can’t wait for it to be over and clear to figure out who they are and try to help them.”

O’Brien and DeBoer checked two students, 8-year-old Fletcher Merkel and 10-year-old Harper Moyski. Neither had a pulse. Adults dragged the most severely injured kids to the center aisle, where a cutout for handicapped seating offered cover. O’Brien took his shirt off to wrap wounds. Someone raided the sacristy and came out with priests’ vestments to hold pressure on wounds.

Another Annunciation dad pulled Sophia Forchas, a gravely injured 12-year-old, out from her pew, pressing towels to her head and holding her hand until first responders arrived.

“You have 4½ minutes of your life, and then you have to live with your actions,” McAdaragh reflected later. “You don’t have time to think. You just do. Your inner you comes out.”

First responders arrived and rushed injured kids to area hospitals. In the gym, O’Brien reunited with his wife, Stephanie, and their kids.

Maybe, he replied.

Or maybe Tom had just provided an example.

A few blocks away, O’Brien’s mother was babysitting McAdaragh’s youngest, not yet a year old. She thought of her brother and Sept. 11. She feared her son was dead.

“It was torture, a feeling of I’ve done this before,” she said.

The O’Briens and McAdaraghs walked back to their homes, which are a couple of blocks apart. Pettee ran into the street. She enveloped her son in a hug, weeping.

O’Brien kept reliving those awful minutes, just like others in that Mass. He wondered how much worse it could have been if the shooter had come inside. He felt guilty he couldn’t do more; two families had lost a child.

Later that day, text messages from Annunciation teachers began popping up in his wife’s phone.

“Your husband is a hero,” read one. “I’ll never forget the moment I saw his face.”

“I’m so grateful Devin was there today,” read another.

“We love you all,” read a third, “and we will get through together.”

O’Brien retreated into himself after 9/11, angry, resentful and alone. He transferred from St. Thomas to St. John’s University, then he spent his junior year abroad in Ireland. He searched for his identity while grappling with a loss as public as it was personal.

The worst thing in grief, he said, is experiencing it alone. Maybe if he’d been in New York City, he would have shared more in the communal grief. Here, 1,000 miles away, it felt like he carried part of the country’s burden. Strangers wanted to connect with him over their own 9/11 memories, but their 9/11 experiences were nothing like his family’s.

This time, the grief is different. So many families experienced this tragedy together. O’Brien leaned hard on his family, his church, his kids’ school, his neighborhood. They’ve seen a gutted community become stronger than ever.

His wife has seen his softer side come out. Watching one of his kids’ fall baseball games, O’Brien burst into tears: grateful for the simple pleasure, devastated some families no longer can experience that. O’Brien and other Annunciation dads at Mass that day talk about their very real survivor’s guilt combined with the very real blessing of this community acting in love and kindness for each other.

“What it has brought out in these men is confiding, being vulnerable, telling you what they’re scared about,” said his wife, Stephanie.

They all confronted the big question: Why?

There is no answer.

O’Brien focused on a different question: What now? His answer, and the answer of the Annunciation community at large, is that the only antidotes for the pain are love and joy and support.

The morning of Aug. 27, both O’Brien and his brother-in-law had a visceral feeling of a cloud of evil coming. But they believe the more powerful story is the courage in what happened after: a broken community picking up its pieces, together. Middle-school kids, alongside this horrific burden, still striving to become kind, ethical, loving humans. Younger kids unable to put words to their trauma but mucking through it anyway, with parents and teachers and counselors by their side.

“That’s the real heroes,” he said. “The courage to live.”