Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Exposition (Initial Situation)
An Irrepressible Bad Boy
Webster opens the play with some very exposition-y exposition: we meet Count Lodovico, who's not even a super-major character, after he's been banished from Rome. He and his pals, Gasparo and Antonelli, chat about the banishment, about what a murderous nut Lodovico is, and about the event that will jump-start the play: the Duke of Brachiano's attempt to seduce Vittoria Corombona. After Lodovico's rap-sesh ends, we're in it: the action starts to rise quickly. The point of this little chat at the beginning involves setting the (very negative) mood, and introducing some basic background info about the main event in the play: Vittoria Corombona's affair.
Rising Action (Conflict, Complication)
Murder, Mayhem, and Courtroom Drama
As the action rises, we see how Flamineo and the Duke of Brachiano scheme to pull Camillo and Vittoria apart—not too hard a task, considering how unhappy their marriage evidently is. The Duke has a secret meeting with Vittoria where he promises to "protect" her from Camillo and Isabella (i.e. murder them). Despite the best efforts of Monticelso and Francisco in trying to prevent the Duke from divorcing Isabella and getting with Vittoria, Brachiano succeeds in his murderous plot: Isabella dies from kissing his picture on the lips (a henchman put poison on it), and Flamineo breaks Camillo's neck, making it look like an accident. This leads Vittoria to get sentenced to a "house of penitent whores"—while the Duke remains un-prosecuted. But she manages to escape with the Duke to Padua, setting the scene for the climax…You can see the rising action as being comprised of all the stuff that cries for revenge, and the climax as being the actual revenge—since this is a "revenge tragedy" after all. There is the sin, and then the punishment for that sin.
Climax (Crisis, Turning Point)
Death By Chocolate… (Or, Actually, Death by Knives… We Were Thinking About Something Else)
The climax comes when Lodovico and Gasparo murder Vittoria and Flamineo. Yeah, you could count Brachiano's murder too, if you want—but he's not quite as central and fiery a presence as Flamineo or Vittoria. (Oh, he's important—it's just that there's some puttering around between his murder and that of the two siblings. So you couldn't really say his death is the peak of the crisis.) The true climax is definitely when, after Flamineo's murder-suicide plan turns out to be a fake designed to test Vittoria's loyalty, Lodovico and Gasparo bust in and get revenge.
Falling Action
Last Words
After Vittoria and Flamineo are mortally wounded, they both make eloquent statements that help sum up the play. As the action falls, they express confusion and uncertainty at death and regret the course of their lives. Vittoria says, "Oh, happy they that never saw the court / Nor ever knew great men but by report!" Flamineo admits "My life was a black charnel," complains about how pointless and full of suffering life is, and finally dies (5.6).
Resolution (Denouement)
Last Last Words
If you thought people were done busting into this room, you were sorely mistaken: after Flamineo busts in, and then Lodovico and Gasparo, finally Giovanni (Brachiano's son, except he's a good guy) busts in along with his officers. They arrest Lodovico for the murders, dragging him off to be tortured and executed. Lodovico doesn't seem too perturbed—really, he's immensely pleased with himself. Giovanni ends the play with a final reminder that crime doesn't pay: "Let guilty men remember, their black deeds / Do lean on crutches made of slender reeds." You know—classic denouement stuff.