The Seventh Enemy - William G. Tapply

When a gun control dispute leads to murder, the Boston lawyer finds himself in the crosshairs in this mystery "that resists simplifying the issues" (Publishers Weekly).
Over drinks one night at his Boston waterfront apartment, goodhearted lawyer Brady Coyne finds himself disagreeing with an old friend about a divisive subject: gun control. Wally Kinnick is no gun nut. But, an environmental activist and hunting expert, he believes so strongly in the right to bear arms that he has come to Boston to testify against an assault weapons ban. When he changes his position at the last minute, he finds himself with a bullet in the gut.
Wally is public enemy number one on a recently released list of opponents to the second amendment; Brady is number seven. To keep himself from becoming another trophy on the wall, Brady must find the men who targeted his friend—before the right to bear arms deprives him of his right to live.