The players play as "Rifts", people living in the titular City who just so happen to have legendary stories living inside of them—their Mythos, which grant them extraordinary powers. Those who don't have these powers are called Sleepers, and they are prevented from seeing anything supernatural by the Mist.
Being a Rift sounds cool, but there are more than a few catches. Not only do you have to deal with all the problems of mundane life, you also have to contend with other Rifts, the enigmatic Avatars and their city-spanning operations, and the Gatekeepers, who are out to destroy you solely for existing. To top it all off, your Mythos has its own agenda, and to fulfill it better (and thus gain more power) you must completely sacrifice your old life.
The game is noteworthy for its unique take on character creation: instead of a few archetypes to choose from, players get four "theme cards" each, all with different classifications. They then write down exactly what these cards do in the form of tags: three Strength tags and one Weakness tag per card. This allows for much, much greater freedom with character creation than in most other Apocalypse Engine games.
This game contains examples of:
- Ancient Conspiracy: The Truth, a group of extremely powerful Rifts dedicated to enforcing Status Quo Is God. Of course, many of them have their own agendas.
- City Noir: The core setting is this trope.
- City of Adventure: Right there in the title.
- City with No Name: The game takes place in The City, and it is strongly implied that it is actually an archetypic representation of the idea of cities. Just like it's inhabitants. It also includes classic locations in a city, like The Docks.
- Extra-Strength Masquerade: The Mist doesn't mean that a Player Character will get away with murder, but Sleepers won't be able to see that the weapon was a magic wand.
- Fantastic Noir: The game has all the trappings of Film Noir (the main characters are detectives, play largely revolves around solving cases, and sessions even start with a voiceover monologue by the players), but with the twist that the people involved have magical powers.
- Fantasy Kitchen Sink: Mythoi can be of any story, from myths to fairytales to classic literature to even real-world events that have attained legendary status. Naturally, that makes the City this.
- Godzilla Threshold: One of the moves you can make, called "Stop. Holding. Back." You make the full use of your powers, allowing you to defeat a threat at a cost determined by how well you roll. This can range from burning all the power tags on a Theme to outright replacing a Theme with one of the opposite kind to just dying. The more Themes you have related to mythical powers, the less control you have over this as you are already riding the edge of diving into your supernatural nature. The range of prices is also determined by the long-term, so if you use this move to, say, kill the major villain of the campaign in one fell swoop... that's probably the Ultimate Sacrifice, and you'll likely have to say good-bye to your character.
- Invisible to Normals: Everything the Rifts can do is covered up by the Mist, keeping Sleepers out of the loop.
- Maybe Magic, Maybe Mundane: The corebooks note that the lead characters never leave the city, and in fact that there doesn't seem to be a world outside the city. They suggest that either the residents are extremely focused on the city or it's another aspect of the Mist.
- Muggles: Sleepers. A Player Character can even become one if they let their Mythos fade away.
- Token Good Teammate: Within the Truth (and, in fact, among all of the Avatars) Ganesha is this—her entire operation is centered around helping people, rather than exploiting them for her own ends. Dr. Leyland counts as well.
- Weirdness Censor: While the Mist is usually what stops Sleepers from seeing the way things are, a Player Character can develop a Weirdness Censor so strong that it prevents Rifts from using their Mythos abilities in the PC's presence.