He Who Walks Beside, most commonly known as Nemesis or the Adversary, is a Walker from Outside that can possess a wide range of entities and affect their minds in significant ways. He was first mentioned to Harry Dresden in Cold Days, but has been involved in the Dresden Files since Storm Front and has been influencing the world for far longer.
I am the doubt that wards away sleep. I am the flaw that corrupts, the infected wound, the false fork in the trail. I am the gnawer, the worm in the book, the maggot that burrows in the mind’s eye. I am He Who Walks Beside.— Nemesis, through Justine
Nemesis manifests as a kind of contagion that infects a person—humans or Supernatural beings—and changes their nature, makes them to act in ways not natural to them and causes them to do things harmful to others. As an Outsider, his goals appear to be inimical to humanity and reality as we know it. Those affected (or infected) by his influence have their natural desires warped into serving sinister purposes.
Nemesis keeps his existence secret by infecting or killing any who appear to know of him, so even speaking his "Nemesis" alias is risky. Those who know of him call him "The Adversary" instead. Infected creatures are able to act against their fundamental natures. For example, infected Sidhe become able to lie. Some or all of the evidence of the Black Council's existence appears to be the work of Nemesis. Finally, the first three major cases Dresden faced — Victor Sells, Agent Denton's hexenwolves, and Leonid Kravos — are all heavily implied by Titania to have been infected by Nemesis.
It is also possible that Nicodemus Archleone mentioned Nemesis during the conversation with Harry Dresden in the Oceanarium. He said “Have you not seen the signs around you? Beings acting against their natures? Creatures behaving in ways that they should not? The old conventions and customs being cast aside?”. These are the exact symptoms of Nemesis, as described in Cold Days. Later in the same conversation with Dresden, Nicodemus refers to what's happening as a "contamination," which in turn is a synonym of the word "contagion."
In the series
In Cold Days, in a meeting at the Botanical Gardens Lily touches Harry Dresden’s forehead supposedly testing for the presence of something. She is relieved to find that he is not infected and goes on to imply that there is a contagion which corrupted Dresden's first three big cases: Victor Sells, the Hexenwolves and the Nightmare. Lily also tells Dresden that her predecessor, Aurora was also infected by He Who Walks Beside and become twisted by him. Maeve arrives and tells Dresden that she is convinced that Mab is infected by the same contagion and intends to destroy the world. The Ladies imply that the Leanansidhe spread the contagion to Mab while she was bound in ice at Arctis Tor.
Dresden summons Titania to ask her if she has noticed any change in Mab’s behavior which may indicate infection by the contagion. Whilst Titania refuses to help directly, she does tell him that the name of the contagion is "Nemesis" and to speak the name carefully, or Nemesis may hear him.
When Dresden visits the Outer Gates with Mother Summer, he realizes that the adversary is an infiltrator who has sneaked past the Outer Gates and is attempting to open them so that the Outsiders may enter Faerie and the mortal world.
During the assault on Demonreach, Dresden is attacked by Cat Sith and realizes the Malk has been infected. Dresden manages to get through to Cat Sith, who fights the contagion for a brief moment, but eventually Nemesis takes over completely. He speaks to Dresden directly, expressing regret that Cat Sith could not remain as a covert asset before attacking him. Dresden blasts Cath Sith with magic and hurls him into Lake Michigan.
After Maeve is defeated, Mab and Dresden discuss the events leading up to that night. Mab explains that spotting the adversary is not a simple task. Lily was not actually able to detect his presence. Even the Gatekeeper, at the focus of his power cannot be completely certain of his presence and influence. Dresden concludes that during the period a few years ago, where Mab was so angry that she could not speak, it was because she found out that Maeve had been tainted. Mab explains that the Leanansidhe had become infected via the athame she received at Bianca St. Claire's ball. The infection was passed on to Maeve before it could be set right. Mab was able to remove Nemesis from the Leanansidhe, and remain unaffected herself, but she could not help Maeve.
- He Who Walks Beside
- This was less a plan than…an act of faith, I suppose you would say.
- Harry Dresden
- He Who Walks Beside
- In what is coming. The unraveling of all things into darkness and silence.
- Harry Dresden
- Empty Night.
- He Who Walks Beside
- — He Who Walks Beside, through JustineEmpty Night. So we pressed the attacks at the Outer Gates. While I sowed havoc within the walls of reality. We loosed some of the primal forces of your own precious Creation against you. Undermined Mab, her people, the Accords, the delusion of order you force upon the universe with your useless presence. You may have survived the day. But the deed is done. We are the tide. Infinite. Unrelenting. And one day, starborn, make no mistake, we will wipe away all that you know.
In Battle Ground, while accompanying her to Demonreach, Harry Dresden notices subtle differences in Justine's behavior and posture, indicating she is possessed. Dresden manages to extract the information that the possessor is He Who Walks Beside, and jumps from the Water Beetle into Lake Michigan, leaving the Walker with the prospect of tackling the island's genius loci without Dresden to help bypass security.
- Victor Sells
- Phillip Denton
- Leonid Kravos
- Vittorio Malvora
- The Leanansidhe
- Cat Sith