How does it feel,
To be on your own,
With no direction home?
--Bob Dylan, "Like A Rolling Stone"
Outcasts are angels who have racked up too much dissonance to remain in Heaven, or who have committed a grievous sin in the eyes of their Archangel and been banished because of it. The demonic equivalents are Renegades.
In terms of game mechanics, an angel becomes Outcast when they first fail a dissonance roll. Once Outcast, an angel is exiled to Earth. He or she may not return to Heaven, use a Heavenly Tether or call upon any of their Superior's Rites. The angel may also expect more than the usual scrutiny from servants of Dominic.
In Heaven, the Heart of an Outcast will crack (but not shatter) and it can no longer be used to track the angel.
Outcasts can call their Archangel, but only when they have gotten rid of all their dissonance, and only to ask that they be restored to Heavenly status again. If the Archangel agrees, the angel's first mission will be one of redemption, to prove he or she can be trusted again.
A character who starts the game as an Outcast must include 3 levels of Discord.