Bill Bryson, portrayed by Robert Redford, is a renowned author who returns to his home in New Hampshire after spending several years in England. His supportive wife, Emma Thompson, whom he met during his time overseas, stands by him. Following a TV interview, the couple attends a funeral, where Bill feels the weight of social obligations. Despite wanting to leave, Catherine encourages him to engage with others present.
Upon returning home, Bill expresses his desire for adventure by announcing his intention to walk the Appalachian Trail — a daunting journey spanning over 2,000 miles from Georgia to Maine. Although Catherine initially expresses her concerns about the trek, she ultimately agrees to let him venture out on the condition that he finds a companion for the journey.
After a series of rejections from potential hiking partners, Bill is unexpectedly contacted by his old friend, Stephen, played by Nick Nolte. This revelation doesn't sit well with Catherine because of Stephen's notorious reputation for infidelity. Nevertheless, she honors her promise, allowing Bill to embark on his expedition.
As they prepare for their adventure, Bill and his son visit a local outdoor store where a charming salesperson, played by Nick Offerman, persuades Bill to purchase various camping gear. Once all set, Bill and Catherine greet Stephen at the airport, where they have a heartfelt reunion amidst hints of friendly rivalry.
Their first morning on the trail proves to be challenging as Bill maintains a brisk pace while Stephen struggles to keep up. Along their journey, they encounter Mary Ellen, a boisterous hiker, portrayed by Kristen Schaal, who believes she knows everything about hiking, much to their dismay. Determined to shake her off, Bill and Stephen hatch a plan to leave her behind early the next day, but she catches up surprisingly fast.
As they navigate through the Appalachian wilderness, the duo faces not only physical challenges but also personal revelations. They endure harsh weather conditions, like a sudden snowstorm, and amusing mishaps that test their friendship and resolve. When they find shelter in a cozy motel, Mary Steenburgen plays Jeannie, the motel owner, who forms a quick bond with Bill, though he remains committed to Catherine.
Throughout their trek, the bonds between the friends strengthen as they share stories and confront the ghosts of their past, including Stephen's battle with alcoholism. Their adventure culminates in life-or-death situations, like a grizzly bear encounter, which they miraculously survive by using their wits.
However, the harsh reality of their journey soon sets in, as they realize they have only covered a fraction of the trail despite their efforts. In the end, a heartfelt goodbye at the bus station leads Bill to reflect on the journey they shared through postcards Stephen sends during his return trip. The last message prompts Bill to ponder new beginnings, leading him to write his latest book, A Walk In The Woods, as he embraces the next chapter of his life.
