This is book 4 of the "Family D'Alembert" series.

This note contains spoilers for the book.

Stephen Goldin, really. #4 of the Family D'Alembert.

This plot doesn't make too much sense. A planet where criminals escape for a while? Well, okay -- but they're totally at the mercy of the people running it, and they seem happy with that risk.

There's probably some plot to use them to overthrow the empire eventually, but that gets rather short-circuited. Helena heads there on her own (the idiot), and some D'Alemberts follow her and dig her out, shutting down this little Garst / Lady A operation before it really gets anywhere.