Then came the role that would unite -- and divide -- Tatum and her father. Cast opposite Ryan as precocious con artist Addie Loggins in 1973's Paper Moon, 8-year-old O'Neal was a novice in every way." I remember practicing lines with my dad, like I'd have to say, 'I love you,' and I'd think, 'I can't say that,' " she recalls. Yet she stole the show -- and an Oscar nomination. "That's when things started getting rough in our relationship," she says. Stricken with a stress-induced ulcer, she became the youngest-ever Oscar winner while her paternal grandparents watched from the audience; Ryan, who was filming in London, didn't attend. "I was happy for her," recalls Moon's director Peter Bogdanovich, "although I knew it was going to be the beginning of a lot of problems."

First, though, there were a lot of parties. Ryan O'Neal didn't exactly shelter young Tatum from the wilds of Hollywood. "When Tatum was 9 or 10, she was a source of embarrassment to all of us older people because she would be brought to these parties where we'd be smoking marijuana," says Ryan's former agent Sue Mengers. "And there was that little face, staring at us with such disapproval. But she had no place else to be." Dependent as she was, O'Neal also pricked her father's vanity. Ryan bet Tatum that his movie Barry Lyndon would beat her 1976 kids' flick The Bad News Bears at the box office. When it didn't, "he started getting crazy and more out of control," she says. "He's got some Irish bully in him and couldn't control his fists." During one fit of rage, "my dad threw a pool cue at my head because my brother was beating him in pool," she says. (Ryan O'Neal declined repeated requests to comment for this story.)

At 13, O'Neal accompanied her dad on location for 1977's A Bridge Too Far, where she says, she was molested by one of his friends. As a result, "I slit my wrists and took a lot of drugs and drank everything in the minibar in an attempt to kill myself," she says. A year later she began experimenting with marijuana and the prescription drug Quaalude. Then, on one occasion, O'Neal's pal Carrie Adelson was driving her to Big Sur after partying with actress MacKenzie Phillips the night before when Adelson crashed Joanna Moore's Jeep on the California coast. "Dad didn't take us to the emergency room," O'Neal says. "He sent a limo."

With scrapes on her leg that required skin grafts, O'Neal spent the next six weeks in the hospital, visited by her Bears costar Walter Matthau and, on one occasion each, her parents. "That was probably the lowest point in my adolescence," she says. Back home, things continued to go downhill after Ryan began his 18-year romance with Charlie's Angel Farrah Fawcett, with whom Tatum had a chilly relationship. She fought regularly with her dad, who, she says, told her at age 15 that she was fat and should use cocaine to lose weight. Their battles continued until one day two years later, when O'Neal says Ryan, angry that she was late for a racquetball match, punched her in the head. "That was it," she recalls. "I didn't see him for years after that."