NORTH KINGSTOWN, R.I. — This is the story of a mischievous mutt who turned out to be a very good girl. Such a good girl, in fact, that she saved a life.

Ruby, an Australian shepherd and border collie mix, ended up in a Rhode Island animal shelter as a pup because of persistent behavioral problems. Five families adopted her in turn, only for each to return her because she was too rambunctious.

“She was a total knucklehead,” said shelter volunteer and dog trainer Patricia Inman, who repeatedly intervened to keep Ruby from being euthanized. “She jumped and bit her leash. She wouldn’t sit or lie down. She just never stopped moving. She was special, and she needed a special person.”

Enter state police Cpl. Daniel O’Neil, who needed a search-and-rescue dog. In 2011, he was taken by an eight-month-old Ruby’s irrepressible energy and intelligence, and after Inman vouched for her, she was trained as a police K-9.

Fast-forward to October 2017, when this tale takes an incredible twist: A teenage boy got lost for 36 hours while hiking, and Ruby succeeded where a human search party failed — she found the boy, who was unconscious and in grave medical condition. He turned out to be Inman’s son.

“Rescued by Ruby,” premiering March 17 on Netflix, tells the story of a problematic pooch who just needed another shot.

“Ruby was given a chance at life and ended up saving a life,” the American Humane Hero Dog organization said in a 2018 citation naming her the nation’s “Search and Rescue Dog of the Year.”

In yet another twist, Ruby is played by a canine actor, Bear, another former shelter dog who was saved by the movie’s dog trainers from being put down.

“It’s a true underdog story,” O’Neil, 41, said in an interview at his office at the Rhode Island State Police, where he now oversees an 18-dog K-9 unit.

“It’s like divine intervention. She was given a chance and she’s been doing everything she can to pay it back,” he said. “You have this dog that was given up on, and she’s changed so many people’s lives.”

O’Neil knew adopting a shelter dog written off as unmanageable was a gamble. Police dogs typically are bred for their work and trained from birth. Most state police K-9s cost $7,500 and come from Europe.

But O’Neil recalls being impressed by Ruby’s determination and focus, and she graduated at the top of her class. And as someone with dyslexia and hyperactivity, he identified with Ruby.

“We both kind of know where each other’s coming from,” he said.

On the afternoon of the boy’s rescue, Ruby led O’Neil straight to the teen, who had tumbled into a ravine. O’Neil’s radio and GPS were out of range, but Ruby’s repeated barking drew authorities to the scene. The youth, who has since recovered, declined to be interviewed.

When O’Neil knocked on the door of the boy’s home to deliver the good news, he found himself face to face with Inman: “I said, ‘Pat, this was her thank you for saving her life — she saved your boy’s life.’ And we both started to cry.”

Later, as it all sank in, Inman found herself wondering: What if?

What if O’Neil hadn’t taken a chance? What if Ruby had been put down?

“I was so grateful. I was beside myself and overwhelmed,” she said. “So many things had to fall into place for this to happen the way it did. The universe works in mysterious ways.”

O’Neil, who’s played in the Netflix film by “The Flash” actor Grant Gustin, said he hopes people will consider adopting a shelter dog.

“If you show them love and compassion and you give them a certain type of stability, they’ll show their true colors,” he said.

Partners for 11 years, O’Neil and Ruby have teamed up on numerous successful rescues and helped convict two murderers based on evidence Ruby sniffed out. They’ve also shared some rough days: In 2020, a drunk driver slammed into their cruiser. Ruby escaped unscathed; O’Neil broke five ribs.

Underscoring the dangers of the work, Massachusetts last month enacted a new law to let first responders treat police dogs injured in the line of duty. “Nero’s Law” was named for the K-9 partner of Yarmouth police Sgt. Sean Gannon, fatally shot in 2018 while serving an arrest warrant. Nero also was shot but state law didn’t allow EMTs to treat him. He recovered and now lives with Gannon’s widow.

Meanwhile, Ruby being Ruby, there’s still the occasional misadventure.

Three years ago, she bolted near a state park, prompting a 19-hour search before turning up safe and sound. More recently, after O’Neil let her out to relieve herself, she returned with a live skunk writhing — and spraying — in her jaws.

“We should’ve known. Ruby’s a down-home girl, not a Hollywood celeb,” wrote Rhode Island Monthly, which featured Ruby and O’Neil in a cover story for its “Rhode Islanders of the Year” edition. “She represents something true and beautiful: We can achieve great things, no matter where we started out in life.”