You can structure a typical 120-minute movie into four acts of 30-minute increments like this:
- Act I — 0 – 30 minutes
- Act IIa — 30 – 60 minutes
- Act IIb — 60 – 90 minutes
- Act III — 90 – 120 minutes
Of course, not all movies are exactly 120 minutes but the basic idea is to divide a screenplay into four equal Acts. One key element is that at the end of Act IIb, the past must somehow catch up to either the hero or mentor.
The reason why you need the past to catch up to the hero or mentor is because part of the hero’s or mentor’s problem is something that occurred before your story actually began. In “Star Wars” and “The Karate Kid,” the mentor’s past catches up with him near the end of Act IIb. In “Star Wars,” Obi-wan has to face Darth Vader after helping him in the past. In “The Karate Kid,” the hero’s mentor, his karate instructor, has to face the loss of his wife in the past.
Most often at the end of Act IIb, the hero faces the past by finally admitting his or her flaw. In “School of Rock,” the hero finally breaks down and admits he’s a failed musician. In “Colossal,” the hero admits that she’s screwed up in the past by getting drunk and being irresponsible. In “Die Hard,” the hero admits that he and his wife separated in the past because he was a jerk.
This is why you need to understand the backstory of your hero and mentor because the past is going to catch up with them in Act IIb and they finally have to face this problem. The past in “School of Rock” is that the hero has lied his way to becoming a music teacher so this past will eventually catch up to him when he admits he deceived the school. The past in “Colossal” is that the hero is a party girl who drinks too much and doesn’t care about her affect on others. This past catches up to her when she sees her drunk boss go out of control by lighting a giant firecracker in his own bar. The past in “Die Hard” is that the hero separated from his wife in the past and now he has to realize he was the cause of the breakup.
The past always catches up to either the hero or mentor in Act IIb. Sometimes the past occurred offscreen such as in “Die Hard” where the breakup occurred before the movie begins, or in “Star Wars” when the relationship between Obi-wan and Darth Vader is hinted at but never shown. Other times the past occurs in the beginning such as “School of Rock” when the hero lies to get a job as a music teacher, or “Colossal” where the hero gets drunk and comes home the next morning, which upsets her boyfriend.
The past plays a huge role at the end of Act IIb because the past is the source of the hero’s or mentor’s problems, and the only way to solve any problem is to face it. At the end of Act IIb, your hero or mentor must face the past and resolve this problem from the past.
When your hero confronts the past, this opens the door for the hero’s eventual change. When the mentor confronts the past, the hero must witness this to help the hero (and the audience) learn from this event so they can eventually redeem the mentor by defeating the villain.
All problems really occur in the past. The end of Act IIb is where this past must be faced, and that moment takes courage, which brings out the emotion in the story.