JUST ONE TINY misstep at mile 15 of the Boston Marathon last spring ruined any chance of amputee runner Jeff Glasbrenner breaking four hours.

He stumbled over a pothole, opening a cut where his running blade attached below his right knee. Glasbrenner cursed his luck as he stopped every mile to clean the wound.

That bump in the road just may have kept the 41-year-old from being in the midst of the chaos. He was three blocks from the finish when the marathon was halted by the two bomb explosions.

“A pothole,” Glasbrenner said, “just may have saved me.”

This year, he’s one of 4,781 runners taking the iconic race up on its offer to return — an opportunity to settle some unfinished business when they line up at the start again.

For many, it’s a chance to finally make good on their months of training — dozens of workouts and hundreds of miles logged — and achieve that finish line. For Glasbrenner, his journey back to Boston became much more than simply finishing.

He’s bringing some company as he trained right-leg amputees Andre Slay and Chris Madison, both whom had never even imagined running a marathon before.

“This is going to be a day filled with lots of joy and tears,” said Glasbrenner, a motivational speaker and three-time Paralympian in wheelchair basketball. “But we’re going to get to that finish line together.”

Glasbrenner has always been a “bucket list” sort of athlete — finish one adventure and move on to the next. He has completed 13 marathons and 22 Ironman triathlons.

So Glasbrenner just had to go back to Boston, to conclude this quest. For himself and for those injured when the twin pressure cooker bombs exploded, killing three and injuring 260. At least 16 people lost a limb or limbs. He could understand the devastation, having lost part of his leg in a farming accident when he was 8 years old.

“I had a hard time watching the news for a few days after Boston,” said Glasbrenner, who was at 25.9 miles — according to his GPS tracker — when police stopped runners. “I’m not going to let a couple of bad guys steal my finish line.”

He talked Slay and Madison into joining him at the starting line. It wasn’t easy: Neither had even run as much as a 5-kilometer race. And first, they had to run a qualifying event (to get into the field for Boston, a mobility-impaired participant has to finish a marathon in less than eight hours).

The trio began training together late last June on paths around Little Rock. At least once a week, they met for a run. On those other days, Glasbrenner gave them a training schedule to follow. He was always a phone call or text away for questions, too.

Slay, 32, and Madison, 39, had plenty: How many socks to wear on their stump? How often to stop and clean the sweat from their prosthetic leg?

And the biggest one: Could they really run a marathon?

“Sure, I had doubt,” Slay said, laughing.

Slay worked at an airline ticket counter when he met Glasbrenner, who frequently travels to give lectures and check items off his sports bucket list. Slay was 24 and finishing flight school when he lost part of his right leg in a motorcycle accident.

First, Glasbrenner attempted to steer Slay toward wheelchair basketball.

No interest.

How about a marathon then?

“Jeff’s like, ‘I didn’t finish Boston. Come back with me,’” Slay recounted. “I was thinking, ‘Well, I guess I can hand you water.’”

“He’s like, ‘No, run with me.’”

The offer came at a good time. Slay was around 240 pounds and suffering from high blood pressure, which put his commercial pilot’s license at risk. This could improve his health.

One slight obstacle: Slay didn’t have a running blade, which costs around $25,000 and isn’t covered by insurance.

No trouble. Glasbrenner had an extra one he could use.

So that’s how Slay found himself at a marathon in Colorado Springs last September, on a borrowed running blade, with only 10 miles of training under his belt, trying to qualify for Boston.

He didn’t stop that day until mile eight, when he felt a blister where the blade attached. One blister soon turned into many more with each step he took.

“My leg looked like bubble wrap,” said Slay, who finished in seven hours. “It was the most excruciating run of my life.”

Those blisters eventually popped and became infected. For six weeks, he couldn’t work, let alone run.

As he recuperated, he received a letter that bolstered his spirits — his acceptance into the Boston Marathon. Then, a prosthetic company donated a custom-made running blade.

“That starting line is going to be so emotional,” Slay said.

Madison feels the same way. At the urging of a friend, he met Glasbrenner for lunch last spring. Madison simply wanted to get some training tips to complete a triathlon.

How about a marathon, Glasbrenner suggested.

“Thought it was a cool idea and fit in with my wanting to do something,” said Madison, who lost his part of his leg when a boat ran into him while he was riding a jet-ski when he was 10. “I didn’t realise the magnitude of what I was getting into.”

Madison attempted to qualify for Boston by running a marathon in Tupelo, Miss., in early September. On a steamy day, with his prosthetic leg just not fitting right, Madison reached mile 25 in 5 hours, 45 minutes. Told the cutoff time was six hours, he decided to call it an afternoon.

Turns out, there was no cutoff time.

“Jeff was so mad. He’s like, ‘I told you to finish,’” chuckled Madison, a former police officer who’s now an attorney.

A month later, Madison ran a marathon in St. Louis and crossed the line in 5:43 to earn his spot at the start line for Boston.

“What I learned is I’m the only one who can prevent me from achieving things,” Madison said. “I’ve achieved the goal of getting to Boston. The next goal is crossing the finish line.”

With Glasbrenner leading the way, of course, eager to finish what he started.

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