Buzz Bissinger’s new book is a physical and metaphorical journey.

Father’s Day: A Journey into the Mind & Heart of My Extraordinary Son (Houghton Mifflin Harcourt) is Bissinger’s account of a 12-day, 3,600-mile cross-country drive he took in 2007 with his then-24-year-old son Zach.

This deeply personal memoir is informed by Zach’s, and Bissinger’s, histories. Zach is the younger of Bissinger’s twin boys, born three minutes after brother Gerry. In those three minutes, Zach suffered oxygen deprivation that resulted in trace brain damage.

Gerry’s life has been “normal” — he is working toward his doctorate in educational administration. By contrast, Zach has an IQ of about 70. He has the comprehension skills of an 8-year-old. He is also a savant with inexplicable skills, including an amazing recall of people’s birthdays and the dates on which the most obscure events occurred, as well as a mastery of maps and directions. Today Zach works as a grocery bagger and an office clerk.

Father’s Day takes the Bissingers’ trip (the itinerary was built around cities in which Zach has lived) and interweaves it with Zach’s complicated story. By the end, the trip becomes a journey of discovery for both.

Bissinger, 57, a former newspaper reporter who writes a column for The Daily Beast, is best known as the author of Friday Night Lights, a nonfiction book about high school football in Texas that became the basis for an acclaimed television series of the same name. Q. You seem to have been very tough on yourself over the years. Did the trip mellow you any?

The pat answer is it changed my life. I’m not gonna say that. I still fly off the handle. I wish I did not, but my buttons get pressed very easily. And Zach always knew that. But we now have a shared experience that is unique and memorable and will remain that way. We always loved each other, but now we also have this common ground.

Q. Who learned more about the other on the trip, you or Zach?

I think I learned more. People have asked that: What did you learn? The things he did, things he liked. Before the trip Zach knew I could fly off the handle. I definitely learned so much about him, in particular empathy, which I’d never seen before. There’s dad getting upset, I’ll be calm. Or him touching my shoulder [in a time of stress]. I’d never seen that.

How observant he is. His ability to soak things up. His yearning for independence. He really wants independence, which shows he’s growing. In Vegas, he said to me, “Dad you have to stop asking me questions because I don’t know how to answer them.” He was telling me, “Dad, you have to respect my privacy, I’m a human being.” That’s fantastic.Q. You got a new view of him.

One thing he did — he brought a picture of my parents [who died four months apart in 2002, deeply affecting Bissinger]. He brought it to L.A. So he takes this picture from a shelf in Philadelphia: a picture from the last time we were all together, and happy — hides it, and brings it out right at the right time.

That enabled me, as best I could, to have some closure with my parents. I was so moved by his sensitivity. In a sense, it’s true. I need him more than he needs me. He makes me laugh. He’s tender, generous, kind. He has a wonderful intellect. He has developed a wonderful life for himself. And to me that’s the definition of character.