Bitter Truth by William Lashner

A stained legal career spent defending mob enforcers, two-bit hoods, and other dregs of humanity has left Philadelphia lawyer Victor Carl jaded and resentful -- until a new client appears to offer him an escape and a big payday. Caroline Shaw, the desperate scion of a prominent Main Line dynasty, wants him to prove that her sister Jacqueline's recent suicide was, in fact, murder before Caroline suffers a similar fate.

It is a case that propels Carl out of his courtroom element and into a murky world of fabulous wealth, bloody family legacies, and dark secrets. Victor Carl would love nothing more than to collect his substantial fee and get out alive. But a bitter truth is dragging him in dangerously over his head, and ever closer to the shattering revelation that the most terrifying darkness of all lies not in the heart of a Central American jungle...but in the twisted soul of man.