Thanks to a microchip, Petey -- the Jack Russell terrier found in Michigan 600 miles from his Tennessee home after being lost for four months -- will be back in his master's lap by Thursday morning.

"He'll fill a lot of lonely hours for my stepfather," Tyanne Morrison said of Petey.

Every morning, Jim Arrighi, 71, took his morning coffee outside in the small town of Erin west of Nashville with Petey sitting in his lap, until the 4-year-old dog disappeared.

No one knows how Petey made it from rural Erin to Rochester Hills, Michigan, which is about 20 miles north of Detroit, said Kevin Hatman, spokesman for the Michigan Human Society.

Morrison said the family always figured someone had stolen the dog, which has a kind nature and likes to go for rides.

"We don't have any ties in Michigan. Petey had gone a little bit out of the yard. He's a friendly dog," Morrison said in an interview on Wednesday.

After Petey disappeared, the family advertised in local newspapers, put out fliers and even used Facebook to search for the beloved lapdog.

But a microchip Arrighi had implanted in Petey made the difference, Hatman said, adding that fewer than 20 percent of missing dogs and 3 percent of cats are ever reunited with their masters.

"Microchips do make it more likely that a pet will be found," Hatman said. "One in three pets go missing sometime in their lives and the chances of them finding their way home aren't very good."

A Rochester Hills resident found Petey in his back yard and took it to a local Humane Society, where a scan revealed the microchip. Michigan Humane Society volunteer Nancy Geiser began the 600-mile trek to bring Petey home Wednesday. The reunion is set for mid-morning Thursday.

Arrighi had to listen to the Humane Society's phone message that Petey had been found three times before it sank in, Morrison said.

"He was dumbfounded. If it hadn't been for the chip, we'd have never have known what happened to him," Morrison said.

The reunion will be especially sweet for Arrighi, whose wife, Juanita, Morrison's mother, died two weeks ago four days before her 78th birthday, Morrison said.

"She loved that dog, too," Morrison said.