3 Act Structure
Each Act of the 3 Act Structure represents a different story goal. The 2nd Act is around twice as long as the others, but the goal remains the same.
The story revolves around three gangs who have feuds with each other, but later accept their differences and fight against a common enemy.
In very reductive terms (and not knowing your story):
- Act 1 – all three are enemies, but evenly matched, keeping them all
- Act 2 (part 1) – they attempt a truce, but it doesn't hold for unresolved reasons (old feuds, holdouts, resistance, mistrust)
- mid-point low – A tragedy forces them to admit they can't keep feuding forever.
- Act 2 (part 2) – resolving their differences, they begin to work together, trust builds. Some who can't accept it leave.
- Act 3 – Combined they are starting to rival the Big Boss, so he sends his top (army? lieutenants?) to smash them before they get out of hand.
Keep the goal of each act clear. It's the lowest common denominator under every character's motivation. They each have different overlapping stories, but they are on the same page with the story goals. Once you cross over to a new act, everyone's goal shifts.
In the 1st act, they are firmly in the status quo. They are full rivals, truce is unthinkable. The inciting event will shake them from the status quo, and force them to try an alliance. Act 1 ends when they are all on the same page with the new goal.
The 2nd act is split in two: a negative arc to the mid-point low, then turning direct and becoming a positive arc, achieving the 2nd act goal.
The 3rd act is an unexpected result of achieving the 2nd act goal, or it is a consequence of rejecting the 1st act's status quo. It is a train wreck that derails the 2nd act gains – there is no more time to 'build positively' or work out differences, they are stuck with the half-rebuilt organization they had going into the 3rd act.
3 Act Structure is not meant to be prescriptive. It is very reductive but clear on this 'main story direction' per act – this is what the characters are trying to accomplish. Those big changes are what make the story feel like it's progressing, not just episodic plot.
With 3 main characters (and a 4th who will steal the 3rd act) you do not have much room to make their organizations complex. Ensembles do not need as much interior characterization, but each MC will need a setup, a twist, and a payoff. There will be redundant side-characters so pick out the important ones and give them unique conflicts with the leaders while doing gang business.