Act III is what your movie is really all about — the battle between the hero and the villain. This is where the hero and the villain’s paths physically cross and only one can emerge victorious.
Act III is the final part of your screenplay and needs to end with a memorable bang that the audience will remember. There should be no new characters or story developments introduced in Act III. Instead, Act III should wrap up all the loose ends of the story and slam them together in a big finale like the end of a fireworks show.
The first half of Act III is where the hero throws himself into the fight and gets closer to the villain. In “Saving Private Ryan,” this is where the American soldiers prepare to hold the town (Inciting Incident), they fight the Germans (Rising Action), and the Americans are slowly pushed out of the town (Climax).
In “Rocky” the first half of Act III is where Rocky finally gets into the ring with Apollo Creed (Inciting Incident), starts getting beat up (Rising Action), and suddenly knocks Apollo Creed down (Climax). In “Finding Nemo,” the first half of Act III is where Nemo’s dad finally arrives at the dentist’s office (Inciting Incident), tries to rescue Nemo (Rising Action), and ultimately fails (Climax).
This first half of Act III is where the hero finally meets the villain and tries to win. The second half of Act III is where the hero ultimately wins or loses. By the end of the Act III, there should be no doubt that the hero won or lost although some films end with an ambiguous finale.
In “Saving Private Ryan,” the second half of Act III starts when Tom Hanks’ character dies (Inciting Incident), the Germans are finally beaten back (Rising Action), and we discover that the old man at the beginning of the film wasn’t the Tom Hanks character but Private Ryan himself (Climax).
In “Rocky,” the second half of Act III begins with Apollo Creed getting angry and fighting back (Inciting Incident), Rocky fighting back (Rising Action), and Rocky ultimately losing the fight but lasting all fifteen rounds, which nobody thought he could do (Climax).
In “Finding Nemo,” Nemo’s dad gives up (Inciting Incident), Dory finds Nemo but she gets caught by the fisherman’s net (Rising Action), and the fish all work together to free themselves (Climax).
The end of Act III shows the hero achieving his or her goal, or losing it forever. The most important part of Act III is that the hero clearly wins or loses and that all loose ends are wrapped up. To make a complete story, all loose ends must be related to the hero’s victory somehow.
In “It’s a Wonderful Life,” George Bailey finally realizes that he has both friends and money, and then Clarence, his guardian angel, finally gets his wings. In “Die Hard,” Bruce Willis finally rescues his wife and the police officer who helped him over the radio finally overcomes his inability to shoot a gun by gunning down the last terrorist who stumbles out of the burning building with a machine gun, ready to kill Bruce Willis.
Where bad movies fail is that they don’t wrap up loose ends mainly because they don’t have any or the loose ends have no relation to the hero’s goal. These loose ends in a good movie simply serve to remind and reinforce the hero’s goal and helps put a stamp of finality to the story. We’re happy when George Bailey realizes how precious his life is, but that feeling gets reinforced when Clarence gets his wings. We’re happy that Bruce Willis rescues his wife and gets back together with her, but that is reinforced by the policeman overcoming his fear and gunning down the last terrorist.
Your ending for your screenplay is most important because it shows how far the hero has come from the beginning. If your hero has changed and taken the audience along for an emotional ride, your script will have served its purpose.