In Oblivion you can join the Dark Brotherhood a murderous band of assassins hired to do contract killings that are brought on by someone performing the Black Sacrement. They only way for someone to make the plea to the Night Mother is to perform the Black Sacrament. The invoker must create an effigy of the intended victim, assembled from actual body parts, including a heart, skull, bones, and flesh. They must then encircle that effigy with candles. The ritual itself must then commence. The invoker must proceed to stab the effigy repeatedly with a dagger rubbed with petals of a Nightshade plant while whispering this plea: "Sweet Mother, sweet Mother, send your child unto me, for the sins of the unworthy must be baptized in blood and fear." So when you accept a contract you are already dealing with a very grim situation. The murders usually involve some type of bonus for yourself if you perform some extra vile deed at request of the performer of the Black Sacrement.