His parents, who had hidden their marital problems, suddenly split up.
"It was decided somewhere in the White House that they would wait until after the 1964 election," Lawford explains, "because you have to understand, my uncle was the first Catholic president, and for my mom to get divorced before my uncle's re-election was not something that anybody really wanted to go through. So they were gonna wait. And then my uncle died. And after my uncle died, my mother was out the door. My parents were divorced, and I began a slide into darkness."
Lawford's mother added "Kennedy" to his name and moved him to New York, a long way away from his father.
"I rarely saw my father after that," says Lawford. "I missed him a lot. I was his only son."
But he gained an extended family: the Kennedys.
"It's like a big gang, like a big Irish gang, and I'm the kid from California who's kind of soft, with a tan, you know? I gotta find my way into this gang. Yikes!" He continues, "It was a lot about, a lot of daring. There was always competition with me and my cousins. We were always boxing each other or playing football."
John F. Kennedy Jr., says Lawford, "was a star in our family, a guy with a lot of grace and a lot of charisma. It was fun being around him."
His cousin, David, son of Robert and Ethyl, closest in age to Lawford, became his closest friend; his Uncle Bobby, a surrogate dad.
"Uncle Bobby was, you know, until his death, from '63 to '68, certainly the head of our family," he says. "My mom was devastated with my Uncle Jack's death and her divorce. And it was hard to control me. But things were holding together until 1968, when Uncle Bobby died. Things just, for a lot of us, just fell apart."
He describes it as watching a balloon lose its air.
"If President Kennedy had represented what our family was, Uncle Bobby represented what our family would become. And when he died, that died. And we were adrift for some time," Lawford explains.
Christopher, 13 at the time, turned to drugs — an addiction, he says, that ruled his life until he was 30 years old.
"I decided, at that point, that the only safety was in oblivion," he says. "I mean, I think at some point, I decided, 'Look, you know what? This world is too scary. I'm going over here. I can control this, and I don't feel quite as much.'"
When he was in law school, he was using Quaaludes, cocaine, alcohol and methadone.
"I would routinely go to bed with many substances in my body," he recalls.
How would he get through a day like that?
"It becomes, you take one of these for this and one of this for that. And pretty soon, you're numb. And I had an enormous capacity to take a lot of things."
In his book, Lawford says his mom, lost in grief and her own problems with alcohol, couldn't help him. His father, still in California, wouldn't.
While he says his father got high with him, he explains, "It was Hollywood. People did a lot of crazy things out there."
Suggest to him that in the normal world, in the middle-class world, you didn't get high with your parents, and he replies, "Right. No. And I would not recommend doing that on any level, ever. It was not good for me. Although at the time, I was thrilled."
Lawford says his genes, the tragedies of his childhood, and pressures that are unique to his family all may have contributed to his addictions.
Lawford: "I think I had a 'dis-ease' in my life that was excruciating, and this was a way to regulate it," he says. When you grow up in a family where the circumstances are so extraordinary and the path so illumed, then finding your own path feels like losing."
Moriarty: "You mean, if you choose to be an actor?"
Lawford: "Or whatever. I was always torn between Washington and Hollywood, my father's life versus my uncles' life. My father's life compared to being one of my uncles is nothing. I mean, my bar was set at dead, martyred president."
Moriarty: "You yourself thought you should go into politics?"
Moriarty: "So why didn't you do it?"
Lawford: "Well, I tried, but drugs and alcohol got in the way. The other thing: there are 28 of us, and there are a lot of people interested in public life. I was never really at the front of the bus on that one."
Lawford says he came close to death four times before he quit using drugs.
"One morning, I woke up, and I fell on the floor, and I couldn't get up," he recalls, "and I called my mother. Now, for me to bring my mother into this horror was obviously a last resort. I remember her coming into my apartment and the look in her eyes, seeing her child who she was convinced was going to die, and she stepped over me to call 911."
But that wasn't even the bottom was it?
"Well, it was one of them," he says. "I bounced a bit."
His beloved cousin, David, wasn't so lucky. In 1984, he died of a drug overdose.
"I miss David," says Lawford. "I named my son after him."
Moriarty suggests: "You couldn't save David, but in some ways, David saved you."
Replies Lawford, "Yes, absolutely. David died, and my father died, and I got sober. I don't think it was a coincidence."
Lawford's stories in his book, and the photos that accompany them, tell just how extraordinary his life circumstances have been. He has had money, contacts and opportunities that most of us can only imagine. But, in the end, his memoir leaves the reader to wonder what might have been.
"Part of my life," he says, "is that I was given everything you could possibly want in life and I squandered it. I'm not proud of that. You know, but I talk about that because I've reclaimed my life."
Now 50, Lawford has been sober for 20 years. And while he has chosen Hollywood, he indulges his political side on the silver screen. He played a mayor in 1994's "Blankman," the vice president in 2001's "Exit Wounds" and an aide in 2003's "Terminator 3," with another famous relative: his brother-in-law, Arnold Schwarzenegger.
But, he says his proudest role to date was commander William Becker in "Thirteen Days," the movie about one of Jack and Robert Kennedy's greatest triumphs: the Cuban Missile Crisis.
This fall, he will appears with Anthony Hopkins in "The World's Fastest Indian."
These days, movies are not enough for Christopher Lawford. He travels the country speaking about drug addiction and plans to write another book. But don't expect anything more about his life or family. That subject, he says, is now closed.
"It was the first book," he says. "It had to be the first book. I can tell you this: I will never, ever again write about this subject (his personal life), right? … I mean, because I've done it. It's done.
"Next!" he concludes with a laugh.