A demon falls in love...

When Scribble gets fired from her desk job in Purgatory, she's completely unprepared for her new assignment on Earth as a Sinister-a demon that tempts a human. Her only exposure to the human world is through the various books she's collected over the years. Her boss, Belphegor, gives her only a few weeks to make her client, Paul Taylor, add enough weight to his soul that he ends up in Hell, but all her attempts to make him sin end up backfiring.

With the help of her mentor, Rotworm, she borrows the body of a succubus to tempt him better; however, she soon starts falling in love with him instead. She must make a decision-give in to her desires and damn him to Hell, or surrender love for the sake of love.

But when she finds out what happened to Paul's previous Sinister, Scribble uncovers clues pointing to a massive scheme by her superiors-one that threatens to tip the balance between good and evil, putting all of humanity at risk! Only an act of love can stop these diabolical machinations, but Scribble and Paul must deal with their dark pasts before they can move forward. With time running out and both Heaven and Hell after them, can Scribble confront the Demon Prince before it's too late... without losing Paul?