Basically Todd is a worried boyfriend and can’t sleep the night after the play because Neil is away and mr perry seemed so mad
So he just, sneaks out and goes to Neil’s house to check
He tries sneaking in from a door/window, whatever, doesn’t matter
The point is than war veteran mr perry hears said door/window open and someone come in, and that wakes him up
He immediately thinks it was Neil who was sneaking out or smth, and very mad goes to his room.
At the same time as this, Neil is in his office, gun in hand, not having yet fired. Neil doesn’t hear him.
Todd managed to get in but is lost because he literally never went to his house before plus it’s dark and he doesn’t dare to switch on the light, plus he’s really trying to be careful to not make noise
When mr perry sees the window open he just puts two and two together, which means than sound of one thing opening and the sound of someone falling equals Neil sneaking out
Mrs perry is still asleep
So mr perry goes around all rooms checking and just like in the movie, enters into the office. Except Neil, startled, gun in hand, sees his father so mad and realizes than it’s either his father or him. Either he dies and breaks free from his father, or his father dies and he breaks free from his father. Was it a rash, reckless decision? Or an accident from being startled while having a gun on his hand? Neil doesn’t know, what he knows is than two seconds later his father is bleeding on the floor.
The noise of the gun obviously scares Todd who forgets about being careful and just runs to where the noise came from, and finds the whole scene before him: Neil, shirtless, still sitting on his father’s chair and just staring in shock, gun still in hand, and his father on the floor, and the red blood.
Anyway they run away after that.