Twilight Sparkle is an intelligent young adult who resents all things evil. She also wishes to end crime in the world and create a utopia in which Celestia reigns supreme. Her life undergoes a drastic change when she discovers the Death Note, a notebook that kills the pony whose name is written in it.

After several experiments with the Death Note, Twilight realizes the notebook's authenticity and encounters the previous owner, a windigo called Avarice. Twilight explains to Avarice her plan of exterminating all the criminals in the world, until there are only people who she has judged to be honest and kind.

Soon, the number of inexplicable deaths of criminals catches the attention of the International Police Organization and the world-famous detective, "P". P quickly learns that the serial killer, publicly known as "Omega", is located in Ponyville and can kill people without laying a hoof on them. Twilight realizes that P will be her greatest nemesis, and begins a cat and mouse game with P.