Will Traynor was a high achieving and wealthy man who enjoyed life to its fullest, whether this was his successful and demanding job, the many adventures he had experienced, or his equally successful girlfriend. However, he becomes permanently disabled due to an unfortunate road accident.
Two years later, Louisa Clark loses her job at the local café ‘The Buttered Bun’. She is a 26 year old, unambitious woman with very few qualifications. Louisa lives with her working class family and is constantly outshone by her younger, more intelligent sister, Treena, who is a single mother. Her parents become disappointed because the entire family depends on her wage. Louisa goes to the Job Centre where Syed, the Job Centre assistant, finds an ultimate option which is to look after a disabled man. Louisa gets accepted and is hired by Camilla Traynor, the mother of the quadriplegic, because she thinks her son needs someone able to brighten his spirits. Louisa notices how falsely everyone is acting in Granta House, Will's family mansion. She later finds out that Mr. Traynor has an extra-marital relationship. However, due to her, Will has become more communicative and open-minded.
Louisa notices that Will's wrists are covered with scars. One day, she overhears Will's mother and sister talking privately and finds out that he tried to commit suicide shortly after his mother refused to grant his wish to end his life through Dignitas, an assisted dying organization. Horrified at his attempt to commit suicide, his mother agrees to honor his wish, but only on the condition that he agrees to live six more months. In that time, she secretly plans to change his mind and show him life is still worth living.
Louisa decides to keep the fact that she overheard hidden from Will and his mother. However, she does end up telling Treena and together they come up with ideas to convince Will to abandon his wish. Over the next few weeks, Will loosens up and agrees on Louisa shaving his beard and cutting his shaggy hair, which he himself had not done in ages. Louisa executes her plans and takes Will to outings, and although Will is significantly happier, she senses that it isn't enough to convince him. Finally, she's overwhelmed and decides she can no longer be a part of Will's assisted death. Mrs. Traynor, however, notices the positive effect she has on Will and pursues her until she takes back the job. In a last and desperate try, Louisa tells Will’s parents and sister that she wants to organize for Will a foreign visit to the island of Mauritius. Meanwhile, the financial situation in Louisa’s family gets worse as her father loses his job, but fortunately, Mr. Traynor offers Louisa’s father a position at the castle.
Will and Louisa end up spending their days talking frequently to each other, her being his caregiver. He notices that she has a very limited life and that her ambitions are quite small, which is the exact opposite of him before his accident. Will tries to motivate Louisa to change her life, to start doing something different and interesting. She's still seeing her longtime boyfriend, Patrick, though they break up, due to his jealousy.
With the help of the internet, Louisa manages to plan a holiday full of adventures for Will in Mauritius. The night before returning home, Louisa confesses to Will that she loves him and kisses him.
On the night of Will's flight to Switzerland, Louisa decides she has to see Will one last time. Her mother opposes because of the same reason Louisa didn't want to work as Will's caregiver at the start, but Louisa gets approval from her father and proceeds. When she meets Will at Dignitas, they both agree that the past six months have been the best in their lives. He dies shortly after in the clinic. Will leaves Louisa a considerable amount of money to continue her education and to expand her horizons beyond her hometown.