Sisters of the Vast Black

Decades prior to the start of the novella, a civil war between Earth Central Governance and its colony planets lead to the loss of Earth's authority. Millions of people died as a result of warfare and biological terrorism.

The Order of St. Rita is a group of Roman Catholic nuns who live on the spaceship Our Lady of Impossible Constellations. The ship is a living organism resembling a slug. They travel to rural colony planets to perform charity work; as part of their mission, they visit a colony on the moon Phoyongosa III, where they bless marriages and perform baptisms.

The Mother Superior is suffering from the early stages of dementia, leading to a crisis among the sisters. At the same time, the Earth Central Governance sends a priest to join the ship's crew, reasserting control over the previously independent sisters. Sister Gemma decides to leave the order when she falls in love with an engineer named Vauca.

The ship received a distress signal from Phoyongosa III; the colonists are suffering from ringeye, a deadly plague. The nuns and Vauca's crew respond, only to find that Earth Central Governance has unleashed the plague in order to trigger another war and regain their power. The Mother Superior reveals that she was previously a member of Earth Central Governance before becoming a nun, and that her husband designed ringeye as a biological warfare agent. As penance, she takes the Our Lady on a suicide attack against Earth's ships. This allows the other nuns to join Vauca's ship, land safely, and save some of the colonists. After this, remaining nuns declare independence from the Catholic Church and vow to continue their mission of servitude and charity.