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 behavioural 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.