Transcript for Chris McCandless' Sisters Return to His Alaskan Home
We turn now to another family secret. Many of you know about the book "Into the wild." We know what he lived through, but do we know what he was running from? Bob woodruff takes us back "Into the wild" tonight. Reporter: The alaskan interior is remote and wild. But there are family secrets that lie buried off this lonely stretch of road. Secrets about a story so many people think they know so well. You start making your way. Very special to take two of my sisters. I'm glad to go back with my sisters -- shelly and Shawna. Reporter: Today, these three sisters are retracing the steps of their famous brother, a young hiker named Chris Mccandless. You three sisters ready? Rock and roll. Reporter: Chris' two-year odyssey across the American west and into the wilderness here was immortalized in a book. And then, an award winning movie called "Into the wild." Is anyone here? Guess not! Reporter: It's the tale of a man -- played by Emile Hirsch, looking remarkably like Chris -- bright, educated, compassionate and full of promise, who gave up creature comforts in search of adventure. I don't need money. Makes people cautious. Reporter: A modern-day Daniel Boone, James dean and Huck Finn all rolled into one. The sisters' journey will be by chopper. After 20 minutes or so, we finally spot it. A bus -- Chris's final stop literally frozen in time. A shrine. It's breathtaking, so very empty. All you can hear is the river. Haunted. Who does this belong to? Wow, I think this is Chris' bible. Reporter: 30 miles from the nearest town, deep in the alaskan wilderness. Chris's goal was to survive here for a hundred days, living off only the land. On day 43 he shot a moose. When he recorded it in his daily journal, he was exuberant. You know he always said, you know, nature might be harsh in its honesty, but it never lies to you. Reporter: But by day 100, he wrote "Death looms." "Too weak to walk out. Have literally become trapped in the wild." He died here of starvation, unable to find enough food. He's been criticized for being selfish and unprepared. He was there without a map, without proper gear and without telling a soul. Still, every spring young hikers make the two-day trek to the bus. It's something about being here brings out something deep within them. Reporter: Chris' voyage has inspired many. A young man who lived by his ideals and gave his life for it. Live before you die. You know, how many of us actually do that? How many of us actually live? Or do we just exist? Reporter: But the sisters say there is something those who admonish and admire Chris don't know. Tonight, for the first time, they tell what they say is a vital part of the story. One that explains why he was here all alone. He wanted to really separate himself from a situation he felt was very toxic. Reporter: It was something Carine didn't want to talk about back in 1997 when "20/20" first interviewed her soon after her brother died. People try to focus a lot on what is was with Chris and why he did what he did and they look for something that's going to be sensational. But of course it's nothing I'm going to get into. Reporter: But now, in Carine's new memoir "The wild truth," she says that Chris' journey stemmed from dark family secrets. The traumatic childhood that she says she and Chris shared. Why did you write this book? Frankly, I was asked every time I met with a group of people why Chris left the way he did. I really watered down those answers for a long time and I really felt and learned that I was doing a disservice to Chris and all those people because the greatest inspiration comes from truth. Reporter: The truth -- Carine says -- doesn't begin at the bus but rather at this house some 3,000 miles away in el Segundo, California. Chris was Carine's adored older brother. He was my protector. He was always strong. He succeeded at everything he tried. Reporter: The mccandlesses were a portrait of happiness. Dad, Walt, was a renowned rocket scientist who had worked for nasa. Mom, Billie, built a consulting business with him. Carine fondly remembers family vacations and peaceful times spent outdoors. Our parents actually got us out in nature. We did a lot of hiking and camping. Reporter: Chris was confident and charismastic. People were drawn to Chris. Reporter: The captain of the high school cross country team, an avid reader, a music lover. But family life for him was much more complicated than it appeared. His father had two families. Both women were pregnant at the same time. I think a lot of women -- people don't realize that. Reporter: Your father really had kind of a double life. He did, but it's funny 'cause even as a little girl that was just what I knew. This was a man that was in and out of our house. He would spend four or five days or how many with us and then be gone for a while. And then he'd come back. Chris and carinne grew up knowing their half-siblings, even going on vacations with them. But their family secret was something darker, something Chris' sisters are talking about tonight. My earliest memories are just you would feel the charge in the air. I mean, it was always there but it would intensify. Reporter: Next, domestic strife brought to life in a movie. He just hauled off and punched him in the spine. Reporter: And secrets between siblings. What drove Chris out into the wild? Letters Chris wrote to Carine before he left that she's kept hidden for over 20 years. I'll be through with them once and for all, forever.
This transcript has been automatically generated and may not be 100% accurate.