A Pinch of Snuff
Splitting a main character into two parts that compliment and confound each other has worked well for mystery writers from Conan Doyle to Rex Stout (and for non-mystery writers such as Patrick O'Brian in his Aubrey/Maturin sea stories). Reginald Hill's unique contributions to this form are his books about two policemen in an unnamed city in Northern England, Detectives Dalziel (pronounced "Dee-al" in the TV version) and Pascoe. Both get to show off their strengths and shortcomings in this wonderfully macabre second book in the series; Dalziel's brawn and instinct meets Pascoe's intellect as the two investigate pornographic "snuff" films in which the actors really wind up dead.