Hazel and Gus are two teenagers who share an acerbic wit, a disdain for the conventional, and a love that sweeps them on a journey. Their relationship is all the more miraculous given that Hazel's other constant companion is an oxygen tank, Gus jokes about his prosthetic leg, and they met and fell in love at a cancer support group.
Famous composer Martin meets concertmaster Barbara at one of his performances, and the two fall in love. After divorcing their spouses, Martin and Barbara marry and begin a happy life together. Five years later, as the couple is working on a new opera, Martin is diagnosed with Alzheimer's disease. As Martin's condition worsens and his personality changes, the couple strain to hold on to the love that once brought them together.