Saturn Apartments has been slowly transitions from SF slice of life to an overarching storyline. This volume in particular is almost entirely taken up by that storyline, about a pair of unemployed lower level scientists building a module to take down to the planet. There's quite a bit more than that going on, including a lot more with the class issues set up in previous volumes. The characters were throughly developed in earlier volumes, and their character growth is remaining true. And really, that's the main draw with Saturn Apartments, isn't it?