On day 200 of a 365 day mission your ship suffers a catastrophic engine meltdown. Stranded in space one hundred light years from Earth, you must make your way back one light year at a time.
It's going to be a long way home.
Jumping from asteroid to asteroid collecting enough dark matter to open the next portal is hard enough, even the tiniest miscalculation can end in death. When you start encountering explosive rocks, micro-comets and teleporting dark matter, things take a turn for the worse.