For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Convict with a Heart of Gold
Ex-con Jean Valjean has some trouble finding lodging or food, since no one's willing to serve an ex-con. Lucky for him, he comes across the house of the nicest man in all the land, a dude named Bishop Myriel. Myriel gives him everything he needs, including all of the expensive silverware in his (the bishop's) house. In exchange, he makes Valjean promise to use the money from the silverware to make himself an honest man. It's an offer Valjean can't refuse, and he goes on to get super rich.
Now that he's rich, Valjean devotes his life to helping others. He meets a poor prostitute named Fantine and stays by her side while she dies of illness. He also promises her that he'll take care of her daughter Cosette, who's living with a stepfamily in a nearby town. It's going to be tough for Valjean to make good on this, though, because a policeman named Inspector Javert tracks him down and tosses him in jail for the rest of his life.
Act II
Just kidding! You're not getting off that easily. Jean Valjean escapes from prison, takes on a new name, and tracks down Cosette, adopting her as his own child (or grandchild, depending on the story he tells). Unfortunately, Valjean soon bumps into Javert and has to go on the run again. He hides with Cosette inside a convent and lives there for the next few years. During these years, Cosette goes from being a child to a beautiful young lady, after a couple of years in an awkward adolescent phase.
Once Valjean and Cosette leave the convent, Cosette falls in love with a young man named Marius. When Valjean finds out about the relationship, though, he gets scared that he'll lose Cosette and decides to move with her to England. Marius finds out, decides that life isn't worth living, and joins his friends in a doomed political revolt. It's not looking good for our star-crossed lovers. Are we headed toward a happy ending, or is this going to be a three-hankie tragedy?
Act III
Jean Valjean intercepts a farewell letter from Marius to Cosette and decides to join the revolt to keep Marius safe. When he gets there, he finds that the rebels have taken Inspector Javert prisoner and plan on executing him. Valjean volunteers to do the job, but he fakes Javert's death and lets him go. Not long after, Marius gets shot and Valjean saves him by sneaking him into the Paris sewer system. Inspector Javert is so confused by Valjean's kindness to him (and by his own decision to be merciful and let Valjean take Marius home) that he commits suicide.
Meanwhile, Marius returns to health and marries Cosette. Once they're married, Valjean tells Marius about his (Valjean's) criminal past. Marius suspects that Valjean murdered Javert, so he decides not to let Valjean hang around Cosette much anymore. Valjean takes fatherly love seriously and starts slowly wasting away.
At the very end of the book, Marius learns that Javert committed suicide and that Valjean is the man who saved him (Marius) from being killed by French soldiers. He takes Cosette and runs to Valjean's bedside. Too late! He says his last goodbyes and dies. Happily ever after? Guess it depends on who you ask.