Villanelle tells the story of a hard drinking but honorable, down on his luck, Travis Burke. After a storied career as Boston Police Detective taking down high profile criminals, Burke has an indiscretion and is compelled to leave his life behind. Making the difficult decision to stay in law enforcement, Burke acquires the position of Chief of Police in the township of New Shoreham.

Sister Kelly Wrath transforms from a nun with a simple temper problem to a vengeful killer. After being gunned down in an alley, she ascends to Heaven to receive training from some of the great figures of religious mythology—Moses, Gandhi, and Jesus Himself. She is sent back to Earth to join the other members of the Order of the Black Habit, a group of supernatural vigilante nuns as they seek revenge against the mob.