Transcript for Teens gather for night of underage drinking at high school party: Part 1
Reporter: It's Friday night. The lights, the band, and the entire town is out to see the toros. Welcome to Spanish fort, Alabama. Population 8,000. Located just east of mobile bay. Once the site of one of the last civil war battles. It will later be the site of a different kind of battle. Very small, close community. Everyone kind of knows everyone. A very tight-knit community, focused on family, centered on very good schools. Reporter: Bible belt churches may dot this small, affluent community but here, football is religion. In Spanish fort, football is no longer a sport. It's a lifestyle. You live, eat, sleep, breathe football. Reporter: No wonder its high school players are celebrated as heroes, says journalist cassie Fambro. People love to see them and recognize them in their community. I would say they're local celebrities. Reporter: And starring in his own highlight reel, running back Cameron Harrison. A senior, 5'7", 180 pounds, wearing number 4. He's small, but he's big. He's hard to bring down. That's one of his advantages. He's tough. Reporter: Among those cheering in the crowd, the new girl in class, 16-year-old Savannah. I am funny, independent, goofy, very goofy, have a lot of love in my heart. Reporter: Among the things she loves, what you'd expect. Makeup, social media and selfies. Lots and lots of selfies. But for the onetime choir girl singing in church with her dad, adolescence brought some big changes. Moving from the only private school she ever knew to unfamiliar terrain, public high school. I cried. I said I don't want to move, but I didn't have a choice. Reporter: Really? I had been at a school from second grade to ninth grade. I loved where I was. I was from the country, there it's so laid-back and small. Reporter: How was the adjustment for Savannah to high school? It was an eye-opener for her. I think it was a huge culture shock. I remember one time she, she called me. She was like, I don't think I can do this. Reporter: Emily and Joe, Savannah's parents, were high school sweethearts. Married by age 20. He, a marine at camp Lejeune. She, a college student studying business. What were your hopes back then? Have a family and have a story. Reporter: But their family's story, the kind every parent of a teenage girl fears, begins on an unseasonably warm October night in 2015. It's Joe and Emily's 18th wedding anniversary. They're enjoying a rare night away from their four kids, celebrating with a romantic weekend in New York City. But meanwhile, back in Alabama, another celebration, an 18th birthday party for one of the Spanish fort seniors. How did this party come about? Everyone was texting about it. Reporter: Haley and Aly, popular high school seniors, say word spreads like wildfire. Even to those outside their usual clique. This was a little bit bigger, and it was lots of different kind of people all mingling together. It was not a typical weekend party. It was probably like one of the biggest parties I've ever been to in Spanish fort. Reporter: Savannah too hears about the party and begs her parents, long distance, for permission. I had the A.C.T.S Saturday morning and the party was Saturday night. Reporter: Just, like, blow off some steam. Blow off some steam. Reporter: You were on the phone with her and what did she say? She said mom, may I go to a birthday party tonight? I said why don't you just stay home, just listen to your inner voice. I just, I want, for some reason I wanted her to stay home. Reporter: But mom's intuition on this fateful night gave way to a daughter's desperate desire to fit in. Me being pushy, finally she was like, okay. Reporter: A tale of two photos illustrate in real time, different nights for mother and daughter. A night out for the parents, while Savannah is seen on Snapchat getting glammed up. With her, a friend. And guess who she knows -- Cameron Harrison, that high school football star. They pregame at his house. The two girls taking this pic in his room. Did you know Cameron Harrison at all? I knew of him. We had math together but I had never hung out with him or anything. Reporter: What did you hear about him? He was just a short little cracker, like just a fireball, just kind of crazy. Reporter: And speaking of fireball, the booze, brought by the kids, flowing freely later that night at this ordinary two-story, four-bedroom mustard-colored house overlooking the timber creek golf course. Now, packed like a nightclub. So how many people were at the party? Probably 40 at one point. Reporter: Make that 41. The birthday boy's 58-year-old grandmother was home, but watching TV upstairs in her bedroom. We walked in and hyped would be the word. There was like rap music playing, hair slinging, and arms flailing. You were just kind of like, wow. It was hectic. People running around, dancing, beer pong, playing video games on the TV. Reporter: And the drinks were flowing? The drinks were flowing. Reporter: Hayden, a senior football player, recalls playing beer pong with Savannah and his teammate, Cameron. She was staring him down, giving him that look. I told him I was like, "All right, she obviously wants it." He was like, "I know, I can tell." Reporter: You had some interest in this guy. I saw you roll your eyes. Why? I always said to my friends I would never with him, he's a nice guy but no. Reporter: 40 underage teenagers partying, drinking, saying turn down, for what. What were you drinking? Smirnoff. I had about two of those before I got there and then I had three or four beers. And then four double shots of fireball. It was under an hour that I had drank this much. Reporter: Others quickly took notice. I first saw her on the couch, one of her friends was like, pouring a little alcohol in her mouth. Reporter: She didn't look like she was completely wasted? No. She was conscious, walking around, having a good time, not stumbling. I couldn't say she might have been able to walk in a straight line, but I don't think most of the people there could've at that point. Reporter: These photos posted on Snapchat may allow us to peer into Savannah's Saturday night, but what they don't show, she says, are the effects of all that alcohol. She says she remembers feeling dizzy but that's about all. What's the last thing you remember? The last thing that I remember is standing in the kitchen with everybody, singing "Happy birthday." Reporter: This is cell phone video of that moment obtained by "20/20." It's like I wasn't even in my body. Like, it's like my head was telling me, like, something's not right, but I just, I could feel myself kind of fading out, like you know, from having control of myself. But that's the last thing I remember was staying in there with everybody. Reporter: Savannah may not remember but her friends do. At one point, Savannah had accidentally knocked over a glass. She looked like something was wrong.
This transcript has been automatically generated and may not be 100% accurate.