The story revolves around the idea that the sun is going to explode and that Earth needs to leave the orbit in order to survive. It sounds a bit complicated and weird, so let me explain.
The sun is apparently evolving into a red sun but in the process of that evolution, there will be a helium flash that would destroy other planets. Humanity notices the situation of the Sun and decides that it is best to leave the orbit and find a new one. They build huge engines called the Earth Engines that will launch them towards a new system called Proxima Centauri. I'll leave a quotation so you can understand the whole plan of humanity.
"Humanity's exodus would proceed in five steps: First, the Earth Engines' jets would be used to counteract the Earth's movement, stopping its rotation. Second, the engines' entire power would be used to set the Earth on a new path, accelerating the Earth into escape velocity, taking it away from the Sun. Third, in outer space, the Earth would continue to accelerate as it traveled to Proxima Centauri. Fourth, in transit, the Earth Engines would be re-aligned, the Earth's rotation would be restarted and the deceleration process initiated. And then fifth, the Earth would be moored in an orbit around Proxima Centauri, becoming its planet. People also called these five steps the “Reining Age”, the “Exodial Age”, the “First Wandering Age” (during acceleration), the “Second Wandering Age” (during deceleration), and the “New Sun Age”. The entire exodus would last 2,500 years, about 100 generations."
Our protagonist is born in the Reigning Age and describes his and also the Earth's journey towards a new life. In the end, we see an older and much wiser man who has seen things. I really liked the story. I wish it was longer than 45 pages because I was just getting ready. Yet, the ending is very good that you do not want to learn what happens next. You can only guess what happens to our protagonist and more importantly, the Earth. As a guy who LOVES Three Body Problem trilogy, this short story/novella was definitely a treat.