What drives attractive male cousins to rape and kill ten young women? Why does an altar girl and her boyfriend lure innocent victims into their customized torture van? Couples who kill comprise only twenty percent of killers -- but they often murder serially and are responsible for particularly inhumane deaths. Sadistic friends, twisted sisters, monstrous couples, and an increasingly pathological mother-son team are amongst those profiled in this exploration of the world's most deviant duos. There are eleven American cases, numerous British cases, and other countries represented in this study detailing depraved criminal behavior. The profiles include California serial killers Leonard Lake and Charles Ng, Laurence Bittaker and Roy Norris, infanticide by New Jersey teenagers Amy Grossberg and Brian Peterson, the British "Moors Murderers", and other profiles of equally scandalous but less publicized murders. Carol Anne Davis explores the formative influences of these killers and their deadly dynamics. She also interviews one of the Wests' surviving female victims and a man who spent time with a serial co-killer now on Death Row.