It's possible that the main characters are an older couple looking back on their life together. They could be reminiscing about all the beautiful times they had, and the story could be told through their memories, with flashbacks to different stages of their relationship.
I'm not sure who the main characters are as I haven't read the novel. But they could be two young people, like a boy and a girl, who come from different backgrounds and find common ground in their shared experiences.