All we know is that Krypton faced destruction, and that is the reason why Kal-El arrived on Earth. Not much of a backstory aside from his parents trying to save their firstborn.
Frankie is a 21st-century computer programmer, turned ufologist when she is approached by the members of the LSS Slicer crew. The starship being commanded by Captain Caldwell. She becomes their most significant asset in the temporal war.
The Slicer was built to map the multi-dimensional wormholes and black holes in the universe. The crew would and go where no one else would dare, as there was no guarantee of ever returning home.
Space is a horrific place when one thinks about it. It’s a vacuum where, if there is no oxygen, life will be sucked right out of you. It is a place where your blood boils before it evaporates. Space is no place for the faint of heart.