In the summer of 1976, Betsy Bailey was at a bicentennial concert in Concord when she heard a familiar voice call out to her.

“Hey you!” the person said from above.

Bailey looked and saw her carefree younger sister, Simone Ridinger, up in a tree.

“I didn’t know she was going to be there,” Bailey recalled. “She didn’t know I was going to be there, and she’s in a tree above me, you know, just no big deal.”

Then there was the timeher sister went all the way to New Orleans for Mardi Gras, even though she was scheduled to work.

“She called to tell me to call her boss, because she wasn’t going to make it in,” Bailey recalled. “But that was Simone. When you say free spirit, that was her.”

The last time Bailey saw her sister was Labor Day weekend, 1977. Bailey went to the Rainbow Restaurant at 9 South Main St. in Natick, where Ridinger worked as a waitress.

“I had lunch at the restaurant, which I normally did on Fridays,” Bailey recalled.

Ridinger, 17, said she planned to go to Martha’s Vineyard and spend the holidayweekend with her mother at a cottage in Chappaquiddick. Bailey asked if she needed a ride to the bus station, but she said no.

After her shift was over, Ridinger changed out of her waitressing uniform, went outside, and started thumbing for a ride, a coworker later told investigators.

But she never made it to see her mother on Martha’s Vineyard. The cottage had no electricity or phone, so she couldn’t have called to say she wasn’t coming. When she didn’t show up, her mother assumed that she had found something else to do instead.

Bailey said she didn’t know anything was wrong until days later whenher mother called to say that her sister had never showed up.

At the time, their mother lived in Sherborn and Bailey was living with their father in Holliston. Ridinger had gotten an apartment of her own at 29 Linden St. in Framingham.

The family notified police that Ridinger was missing and began searching for her. Their father organized a group of people with CB radios to search along the roads she could have taken to the ferry.

“They kind of did a relay from Framingham all the way to the Cape. His friends on their CBs, checking the sides of the road,” Bailey said.

Bailey said her mother gave her a list of things to do. One of her tasks was to pick up some pictures an amateur photographer had recently taken of her sister.

“I’d never met him,” she recalled. “Somehow he got in touch with our mother and said he had these pictures.”

Bailey went to a home in Framingham, where the photographer was apparently living in the basement of his parents’ house, she said.

“I remember going down in the cellar,” she recalled. “Which is just a little creepy when I came to think about that, years later. But then I didn’t. I was just getting the pictures. But that was the one and only time I ever met him.”

For a long time, Bailey and her family held out hope that Ridinger had ventured off somewhere on her own. But they never heard from her again.

In 1986, a 79-year-old man came forward after seeing a newspaper article about Ridinger and told authorities that on the morning of Sept. 3, the day after she was seen leaving work, he was driving to Barnstable to pick up clock parts and was pulled over by a State Trooper on Route 128.

The man said the trooper had a girl in his cruiser and asked if he could give her a ride to Cape Cod. The man agreed to drive her and said he dropped her off at a rotary in Hyannis, just off Route 28, police said.

His description of what Ridinger was wearing matched what her coworkers saw her wearing that day — information that had not been made public before. But investigators were never able to corroboratehis story, according to Andrew Richard, a Sherborn police detective.

Richard said State Police have been unable to confirm the traffic stop ever occurred, and the man who claimed to have given her a ride has died.

The amateur photographer has also died, he said.

“We’re still actively investigating it,” Richard said. “Unfortunately, it heavily relies on people coming forward with information.”

“We have a couple of people of interest,” who were regulars at the Rainbow Restaurant, he said.

“One of our theories is that she never left the area,” Richard said.

Sherborn police are seeking information about anyone who may have lived with Ridinger in Framingham; customers who frequented the Rainbow Restaurant when she waitressed there; and anyone who may recall a female hitchhiker getting picked up in Natick and dropped off in Sherborn, Framingham or Cape Cod. Contact Sergeant James Godinho and Detective Andrew Richard at 508-653-2424 or email them at [email protected] and [email protected].

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Emily Sweeney can be reached at [email protected]. Follow her @emilysweeney and on Instagram @emilysweeney22.