The world of Dragan Sakic, a troubled emergency room physician, begins to fall apart when he proves that the death of Salt Lake City’s District Attorney was murder. The medical examiner is about to sign the death certificate when Dragan points out that three substances found in the DA's body, no more than natural remedies when taken separately, mimic a heart attack when combined. A tiered poisoning?
In providing an ailing investigation impetus by revealing additional suspicious deaths for what they really are—elaborate poisonings—Dragan makes himself a target. When his girlfriend Nina, an investigative reporter, is found near death, and evidence discovered at their home implicates Dragan in the DA’s murder, he becomes the prime suspect of the investigation, and in Nina’s attack. Framed for murders he did not commit, and faced with the loss of the person most dear to him, Dragan is thrust into a shady world of betrayal, revenge and religious zealotry.
This isn't specific enough to hook me but I like the idea of tiered poisoning a lot. You need the villain to rear his ugly head, or it's too lopsided.