Blue Blood — Max Allan Collins

When a pair of armed intruders bursts into Detective Andy Sipowicz's apartment, he quickly concludes they are out to get him, and that he has put his new wife in danger. But everyone involved in the case believes Andy's wife, a prosecutor who has made plenty of enemies herself, could just as easily have been the target. Soon they will all find that the cold, hard truth is far more complicated, as it becomes quite clear that nothing is as it seems.