Protagonist from roughly our-ish time frame wakes up with no memory. On a spaceship. Nearly at the end of a trip to another star (like, wut, he knows we don't have the tech for that). He slowly recalls that our sun is inexplicably dimming which will basically end life on Earth in a matter of decades. But why the heck is he way outside of our solar system and how tf is that even possible?

Obv dude has to figure out what his mission was and somehow save our sun.