The lawyer doesn't just hire killers to do the deed for him. He and a scientist have come up with an approach to murder that looks like "natural causes" (or so the agent suspects), and spends 512 pages trying to prove it.
The story doesn't bare much examination, but it rattles along at a quick enough pace for you not to realise quite how dumb it is for long periods. Iles won't win a Pulitzer for it but it's a fun read all the same.