Harold Fry is a retired sales representative who is living a mundane and unfulfilling life with his wife, Maureen. They have grown distant from each other after their son David left home and their relationship became strained. One day, Harold receives a letter from Queenie Hennessy, an old colleague with whom he worked in a brewery twenty years ago. She is terminally ill and writing to say goodbye. Harold writes a letter to Queenie and sets off to post it. However, on the way, he decides to walk to the hospice where she is receiving care, believing that if he walks the 450 miles from his home in Kingsbridge to the hospice in Berwick-Upon-Tweed, Queenie will stay alive.
During his journey, Harold meets various people who offer him food, shelter, and encouragement. He also encounters challenges such as inclement weather, sore feet, and moments of doubt. Nevertheless, he persists in his pilgrimage, fueled by the belief that he must save Queenie. Along the way, he reflects on his own life, the mistakes he has made, and his relationship with Maureen. He calls her every night to update her on his progress, and she gradually warms to the idea of him completing his journey.
Eventually, Harold reaches the hospice, having raised awareness and support for Queenie's illness along the way. He is surprised to find that Queenie has already passed away, but he is able to speak to her sister and say goodbye in his own way. He also reconciles with Maureen, who has come to meet him at the hospice, and they begin to renew their relationship. Harold's journey has given him a new purpose and a new perspective on life, and he returns home a changed man.