During the argument, it is revealed that Vincenzo is actually Didi's real father, and as the fight escalates, Kat pulls out a gun, points it at Johnny, and then turns it on herself.
Vincenzo is actually Didi's real father. This was what it is revealed during the argument. Kat pulls out a gun. This is during the argument. Kat points it at Johnny. This is during the argument. Kat turns it on herself. This is during the argument. The fight escalates.