True Detective (a Nathan Heller novel) by Max Allan Collins is $2.99
I think this is the first of the Nathan Heller series, for which Collins won a Shamus award. The series is set in the 1930's, and feature a blend of detailed and seemingly accurate history of the organized crime of the period with a fictional detective. Well done, if it's your cup of tea. Although I eventually grew tired of the series, I really enjoyed the first several I read. (To be clear, I do think the writing quality remains excellent on the later books, just not quite my preferred style.)
Mortal Sin, by Paul Levine is $0.99
This was free a couple of times early last year, but it's quite enjoyable if you missed it.
from Library Journal
"Lawyer Jake Lassiter is defending Florida real estate developer Nicky Florio in a civil suit regarding an environmentalist's death at a poolside party. ... (Lassiter) ...finds himself witness to a beheading, accused of embezzlement and murder, and on the run. Indian rights, animal rights, and slimy politicians and lawyers all surface in this fourth Lassiter novel. Permeated with cynicism and the corruption of South Florida that recall the work of Carl Hiaasen, this thriller races to a smashing climax."