Walk the Wire by David Baldacci 

In which the main characters of the Memory Man series, Amos Decker and Alex Jamison, team up with the main characters from another series, Will Robie and Jessica Reel.  Decker and his partner get sent to London, North Dakota to look into the death of a woman, without any background information about her or why they are being asked to solve the crime.  She was found by a man hunting a wolf.  The town is embroiled in a fracking boom.  Then the man who found the corpse comes-up missing.  Decker discovers a clue relegated to a minor section of the autopsy report.  Then another woman goes missing and when Decker returns to the house of the missing man, he finds the woman dead in a shed.  When he confronts the part-time coroner, the man commits suicide.  Then one of the two richest men in town buys the other out and is found dead in his car, an apparent suicide.  Then the other rich man is found in his office, an apparent suicide.  Decker doesn’t like coincidences.  He is followed into an alley and is tackled, by Robie, which saves his life.  They team up to run down what looks like the real motive for the murders, busting up an attempt to poison everyone in a hundred-mile radius.  Only they didn’t kill the people Decker is investigating.