The Fallen appear as slender dark shadows difficult to distinguish even in Uriel's light. They are adept at using a mortal's own inclinations against them in order to make choices they wouldn't make otherwise. They know how to add enough anger, self-recrimination, guilt, and despair into the mix, effectively taking a mortal's free choice from them in an insidious way.
A group of Fallen Angels has formed the Order of the Blackened Denarius and taken human hosts. The Fallen themselves are what makes the Denarians dangerous, more so than their abilities, goons or guard-dog-creatures. They are older than time and have spent thousands of years learning the ways of the mortal world and mind until they understand things humans can't grasp. They know every trick and move, and they are riding shotgun with each holder or in the driver's seat. The Fallen have a perfect memory and a vast library of information.
In the seriesEdit
In Death Masks, Harry Dresden speaks of the Fallen to Karrin Murphy when discussing Demons. He tells her that the real, "Exorcist"-style, demons, are called The Fallen and that they are not free in their actions, as other kinds of demons are. He does not know why this is so, but it could be either advanced magical resonance theory or simply because "God said so".
Shortly after, Dresden runs into his first Denarian, Ursiel. After it is defeated, he asks Michael Carpenter if it was one of the Fallen, to which Carpenter nods and when Dresden responds that the Fallen aren't allowed to act in such a way, he replies that some are. Dresden says that the Fallen aren't allowed to take away free will. Carpenter agrees, but adds that they can tempt, and then introduces him to the Order of the Blackened Denarius, saying that those particular Fallen inhabiting coins have a lot to offer in the way of temptation.
Lash tells Dresden that all of the Fallen know how it feels to "think of someone who would dictate your every move, impose upon you a code of behavior you could not accept, and refuse to allow you choice, expression, and the pursuit of your own heart’s purpose."
In Small Favor, Harry Dresden informs his "War Council" that it is the Fallen that make the Denarians dangerous. He describes them as beings older than time who have spent two thousand years learning the ins and outs of the mortal world and the mortal mind.
When Dresden asks Michael Carpenter if the Fallen can overwhelm someone and possess them without consent, he replies there are some circumstances that can lead to such a possession. Mental damage, drugs, dark rituals, extended deliberate contact with spiritual entities and a few other things can open a soul to possession.
According to Dresden, the reason Denarians don't like going into churches is because it makes the Fallen feel. It makes them remember and makes them sad.