The Gotham mob is broadcasting what they hope to be Two-Face's execution, and Batman is running out of time. Bruce knows Erin is leading him on, not telling him where Harvey's been taken in hopes that the mob gets the job done, but she eventually says he's being held at the old courthouse... Which Bruce doesn't believe, because he notices the "U" in word "Justice" on the court seal is just a regular "U," where the actual seal uses a Roman "V." So Bruce ejects Erin from the car (leaving her for the cops) and knows where to find Harvey, at an old stage lot.
Before the mob can burn Harvey alive, Batman shows up to rescue him, while trying to get through to Harvey with the whole "you used to stand for something" speech, while saying he could have channeled his anger into something good... at which point, Harvey drops a bomb and says "Like you did, Bruce?!" Turns out Harvey knows just who Batman is, and reminds his old friend that he pushed him into becoming the DA, which set off every event that's lead to their current predicament, and effectively killing off the Harvey Dent that Bruce once called a friend.
Bruce doesn't believe that Harvey Dent is gone, claiming him to be on the third side of the coin, the edge, where both the other sides meet. While Bruce deals with all the mobsters trying to shoot them up, Harvey gets a hold of a flame thrower, and just starts lighting up the place, forcing Bruce to up the water tower on top of the building to douse the flames.
After a flashback to when Harvey and Gilda met, Harvey is washed out the stage, where he comes across Gordon, shooting him in the shoulder. Harvey tells Gordon that he's the only good man left in Gotham, and to make a choice between taking him in or letting him go, which isn't much of a choice for Gordon. So Harvey gives himself a choice at the flip of a coin. Heads, he surrenders, tails he kills Gordon. The coin lands in a pile of dirt on its edge, which leaves Harvey unable to actually do something, just yelling in frustration until Batman shows up, leaving Harvey to make an escape on a police motorcycle, while Bruce tends to Gordon's gun shot, which nicked an artery.
Gotham has settled down. While Erin is in prison, making a few friends, Harvey has gone back underground, and is once again playing a game of Russian roulette. But instead of flipping the coin, Harvey puts the coin on its edge and spins it, putting the gun to his head. Before the coin lands on one said, a gunshot is heard, and blood splatters Gilda's portrait...
Elsewhere, Batman shows up to the GCPD with a new Batsignal, and speaks to Gordon about Harvey going deep underground, and despite Harvey seemingly being lost, they will continue to fight the war together.