A small town famous for being the childhood home of Mark Twain is stirring headlines for a more sinister reason.

The disappearance of Christina Whittaker from Hannibal, Missouri, is the subject of a new true-crime docuseries on discovery+ titled "Relentless." It details a filmmaker’s obsession with finding out what really happened to the 21-year-old who vanished on November 13, 2009, leaving behind a 6-month-old baby girl.

Christina Fontana’s quest began in 2007 while working on a separate documentary on families of the missing from across the country. In 2010, she met Whittaker’s parents, which left a lasting impression on Fontana that couldn't be ignored.

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Christina Fontana traveled to Hannibal, Missouri to learn about Christina Whittaker's case.

Christina Fontana traveled to Hannibal, Missouri to learn about Christina Whittaker's case. (discovery+)

"The thing that struck me so much about Christina’s story and case was the passion and the tenacity that her mom had for finding her - and she had active leads," Fontana told Fox News. "She was out there with her husband following up on those leads. They felt like they were on their own. They are just so passionate about finding her. I got caught up in that passion and that’s why I shifted a lot of my focus from the original documentary into Christina’s story."

Families and loved ones described Whittaker as "completely full of life" who was kind to everyone she encountered.

"No matter what was thrown at her, she always had a smile," said Fontana. "She was always trying to make people laugh. She always wanted to take care of the people around her. She was a very warm, loving, trusting person."

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Christina Whittaker, seen here with her mother Cindy Young, is the subject of a new true-crime docuseries.

Christina Whittaker, seen here with her mother Cindy Young, is the subject of a new true-crime docuseries. (discovery+)

Things took a dark turn on the night of November 13, 2009. According to Fontana, the young mom had gone out with a few friends. Whittaker, who was believed to be intoxicated, got into an altercation with someone at a bar and was asked to leave. She was then separated from her friends and was last seen at another bar closer to 1 a.m.

"She had come alone, visibly upset and she was on the phone arguing with someone," said Fontana. "The bartender had asked her, ‘Do you need anything? Would you like a ride home?’ And she said, ‘No, I’m OK.’ And ran out the back door. The next morning, her phone was found on the ground. That was the last time anyone had seen her."

Whittaker was last seen outside Rookies Sports Bar, KHQA reported. According to the outlet, the Hannibal Police Department said it interviewed more than 200 people during its investigation. Lt. Jennifer Grote noted that FBI agents even came to Hannibal two months into the case to investigate. In addition, HPD conducted interviews with prisoners behind bars for other unrelated crimes.

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Christina Whittaker went missing on November 13, 2009.

Christina Whittaker went missing on November 13, 2009. (discovery+)

The outlet also noted that Hannibal police said they've worked with 45 agencies from across the country in hopes of getting leads.

"What I find so intriguing about this case is that on the surface, it really did seem like there was this girl who was in the wrong place at the wrong time," Fontana explained. "But once I started scratching underneath that surface and uncovering these layers to Christina’s life, there was so much more to the story. There are allegations thrown at almost everyone in Christina’s life, including the family and the police."

"There are also a lot of what-ifs flying around," Fontana continued. "Maybe she wanted to leave home because of certain things. Maybe people wanted to harm her because of certain activities that were going on in her life that we uncover in the show. This is a very small town of about 17,000 people. When you engage with the locals, they all have one thing in common to say - there are a lot of rumors in Hannibal. And nothing is what it seems."

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Christina Fontana said a lot of surprising revelations about Christina Whittaker's case were made in the docuseries.

Christina Fontana said a lot of surprising revelations about Christina Whittaker's case were made in the docuseries. (discovery+)

Fontana said that in 11 years, she obtained more than 400 hours of footage from field investigations and video diaries. She was willing to follow up on nearly every tip in hopes it would lead to answers. She also highlighted "diary camps" where Fontana would get emotional over roadblocks she faced in her own investigation.

Fontana said there were many moments, long after cameras stopped rolling, that Whittaker’s case haunted her. Fontana became so immersed with the story that she found herself at times breaking down suddenly.

"It was very hard to sift through all that," Fontana admitted. "And the family didn’t want to put everything out there because they were afraid people who knew the truth wouldn’t want to speak out or go in hiding to avoid attention. And you had people who were trying to manipulate things for their own reasons. I think that’s what’s stopping us from getting to the truth faster. Things aren’t so black and white, as audiences will learn in this series."

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Cindy Young is hopeful that Christina Whittaker can still be found.

Cindy Young is hopeful that Christina Whittaker can still be found. (discovery)

Despite hundreds of theories, Fontana said Whittaker’s mother has her mind made up.

"She very much still believes her original theory - that Christina was asking people for a ride home, which there are witnesses to attest to that, and she was picked up by some men, brought to Peoria, Illinois and was being held against her will and put into sex trafficking," said Fontana. "She firmly believes that Christina was brainwashed into thinking that she could never go home. That's why she hasn’t returned home to this day."

Whittaker still remains missing but not all hope is lost. Fontana said that since the documentary premiered, there have been new leads. She believes that in time, the world will know what really happened to Whittaker.

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Christina Fontana spoke to many of Christina Whittaker's loved ones for her film.

Christina Fontana spoke to many of Christina Whittaker's loved ones for her film. (discovery+)

"It’s the hopeful part of me," she said. "We have some pretty big revelations in the latter part of the series. And I really do believe that we have pushed the case forward. Ever since our first three episodes dropped, my phone has been ringing off the hook with calls from people in Hannibal who want to come forward after seeing it. So I do believe that people with direct knowledge of the case will start to see those people being brave and say, ‘I’m not alone. I will also come forward.’"

Fontana added that the town of Hannibal shouldn’t be blamed for the vanishing.

"I have to say that Hannibal, Missouri is a really beautiful place," she reflected. "The residents are very warm and welcoming. And they do care about what happens to their own."

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The town of Hannibal, Missouri, the childhood home of Mark Twain. According to the Mark Twain House & Museum, the writer moved here when he was 4 years old.

The town of Hannibal, Missouri, the childhood home of Mark Twain. According to the Mark Twain House & Museum, the writer moved here when he was 4 years old. (discovery+)

Today, Fontana is grateful that the documentary is out and being shared among those who are learning about Whittaker’s disappearance for the first time. But the search isn’t over.

"I’ve been on an 11-year journey," she said. "It has never turned off for me. I wasn’t just shooting and then going back to my life. I became very connected to Christina, a girl that I’d never met. She really did become a very big part of my life. And I will continue to push forward. It would mean everything to see this through, to get justice for her."

"Relentless" is currently available for streaming on discovery+.