Blurb from a JoCoNaut:

Book 1 of the "Janitors of the Post-Apocalypse" sci-fi series: it's a light and funny read with a serious side. The humans who survived the zombie plague were discovered by the squid-like Krakau, who found a way to cure limited numbers of humans to serve as low-ranking troops in their space fleets. The story begins when a bioweapon leaves one ship's human cleaning crew as the only ones left to run the ship, discover a conspiracy, and try to figure what happened on Earth all those years ago.

Content warnings include Mild to moderate violence; not much gory stuff.