Carl Colby has an intriguing subject in his new documentary, “The Man Nobody Knew”: his own father.

That would be William Colby, director of the CIA from 1973 to 1976, a towering figure of Cold War espionage who famously disclosed the agency’s “family jewels” in congressional hearings that wound up leading to his replacement.

On ABC’s “Top Line” today, Carl Colby recalled what it was like growing up with a father who kept every detail of his life shrouded in secrecy.

“I knew he was always doing something special. He was tasked with a mission, and in our family, you know, you didn’t get straight answers to: Where are you going? Or where have you been?” Colby told us. “And you take it on sort of faith and trust that what he’s doing is the right thing.”

Colby interviewed, among others, journalist Seymour Hersh, former national security adviser Brent Scowcroft, and former Defense secretary Donald Rumsfeld to illuminate his father’s world.

And he found another rich resource in his own mother, who was also interviewed for the documentary:

“For her, we’d always been in this club, or at least, supporting the membership of the club. My dad is in the club, we’re just sort of supporting the membership,” Colby said. “I think she kept us all to a really high moral standard, and that’s where my parents really connected I think initially. And that’s where they diverged in the end.”

There are lessons for the current president in his father’s experience, Colby said.

“The president is setting the actions so now,” he said. “It’s as if the American people obviously are very supportive of the CIA taking out bin Laden and the senior figures. But you have to wonder, you know, one more drone attack or attack on the New York City subway system, will the CIA once again be dragged before Congress for hearings as to what happened and aren’t you out of control?”

So I think the task of the president, this president as well — even though his hands are full, got a lot on his plate — is to explain the war to the American people and explain this kind of war, this secret war, and why it’s necessary. Because otherwise, there are going to be people at the agency now, including the very top, who are going to suffer the fate of my father — which is to be basically used up and thrown away.”

The film is opening up on a rolling basis at theaters nationwide. Check out the film’s Website for information on where you can watch it.