All the scientists are being bussed down to a spot twenty miles away from the Trinity test site to watch the test from a safe distance.
Ted Hall haz a sadface because he wasn't important enough to get bussed down to the test. He's been assigned to an army rescue crew who will help evacuate people from nearby farms/towns in case of radioactive fallout.
Groves seeks out Oppenheimer, and together they assess whether the weather is clear enough for the test to go on as planned. They postpone it about an hour based on reports from their head meteorologist.
Kisty, Bainbridge, and the few remaining scientists arm the bomb and jump into running jeeps to flee to Oppenheimer's bomb shelter, where Oppie and his control room are located six miles away from the blast site.
A physicist in the control room announces that the bomb is armed and they have twenty minutes until it's supposed to go off.
Everyone is instructed to lie down in the sand, look away from the blast, cover their heads with their arms, wear sunscreen (you know—as protection against a nuclear bomb…because that should work), and so on but most of them are determined to see the whole thing.
The scientists are all given dark welder's glass to look through to protect their eyes.
Those in the control room anxiously count down the seconds until the bomb is supposed to detonate, worried something won't work.
In his impatience, Kisty jumps up onto the top of the bomb shelter and put on dark glasses because he thinks he's at a safe distance from the blast.
Then, as the countdown hits zero, it's like the sun is suddenly shining where it was pitch-blackness a second before. But it's a sun that's way, way brighter than usual.
There is a wave of heat blasted with the light, like "opening a hot oven."
The scientists all watch the magnificent ball of fire roiling into the sky and are relieved and happy that it worked.
The sound of the blast comes thirty seconds later and knocks Kisty off the top of the bunker.
They all start celebrating, cheering, yelling, and drinking whisky out of paper cups.
Then, a few minutes later, the realization that their wonderful experiment is going to be used as the deadliest weapon in the world hits them, and a silent chill rushes over them all.