Prison time is HARD TIME any way you look at it. But it's hardest of all when the prisoner is serving a sentence that allows no flexibility at all, no matter what the circumstances. Our Cover Story is reported by Erin Moriarty of "48 Hours":

"We had tried calling the cops," said Lee Wollard. "We had tried doing everything. Nothing worked. Nothing."

After hearing 59-year-old Wollard's story, you may think he did what any family man would do.

Or, you may agree with a Florida jury and think he went too far. But either way, you're likely to wonder: Does Wollard's punishment really fit the crime?

"Never, never in my wildest dreams did I think I would be here," he said in prison. "I still have a hard time believing it. It's unbelievable!"

Lee Wollard's troubles began six years ago. He was a professional with a master's degree in Davenport, Fla., living with his wife and their two daughters and working at Sea World. When his youngest daughter Sarah began dating a troubled 17-year-old teenager with no place to live, Wollard and his wife, Sandy, took him in.

"You know, if someone needs help, we'll help 'em," he said.

Moriarty asked, "Did it go OK, initially?"

"For about a week," Wollard laughed.

Sandy Wollard said, "It started out his behavior was fine. I'd ask him if he would take the garbage out or clear off the table, and it was, 'Yes, ma'am,' 'Yes, ma'am.'"

But Sandy says the relationship with the boy, whom we agreed not to identify, soon soured.

"This young man was taking my daughter out at night, after we had put her to bed and we had gone to bed," she said. "And he was disappearing with her. And he would disappear for days at a time with her. And she was 16 years old."

The Wollards asked him to leave, but nothing kept him out of the house -- until May 14, 2008. As Lee was taking a nap, his daughter and her boyfriend began to fight.

He heard a loud noise: "Like you were throwing stuff against the wall," said Lee.

Then came cries for help. "It's not like my family to ask for help. So I grabbed my .357 and loaded it with shells," said Wollard.

"That's a large gun," said Moriarty.

"It's a heck of a gun, yes," said Wollard. "You even wing someone with a .357, they're in deep trouble."

According to Wollard, the young man lunged at him and punched a hole in a wall; the teenager disputes that. But no one disagrees about what happened next.

"So I fire a warning shot into the wall, [and] I said, 'The next one's between your eyes,'" said Lee.

Sandy continued, "And the kid turned around and just hurried out the door. And that was the end of that."

Not quite.

Wollard was charged with shooting into a building with a firearm, aggravated assault, and child endangerment. And when he went on trial a year later, a jury convicted him of all charges -- and then Judge Donald Jacobsen sentenced him to 20 years in Florida state prison, the mandatory minimum.

That means Wollard will serve every day of 20 years in state prison.

"And I was just like, 'What?'" recalled Wollard. "You know, the blood just drained out of my head. I almost passed out."