Season 1

1. Book I: Genesis

After serving four years in prison for a drunk driving crash that killed a young woman, Riley Flynn returns to Crockett Island, a fishing village devastated by an oil spill. Having lost his faith in prison, Riley struggles to reconnect with the island’s devout Catholic community, including his parents Annie and Ed, his brother Warren, his pregnant former girlfriend Erin Greene, and parishioner Bev Keane. A young priest, Father Paul Hill, arrives as a temporary replacement for Monsignor Pruitt, who is reportedly on pilgrimage in the Holy Land. While out at night with friends Ooker and Ali, Warren sees strange movement on a remote island inhabited by feral cats, one of which is later mauled by an unseen entity. The next night, Riley sees a figure resembling Pruitt walking along the beach during a storm before it disappears. The following morning, hundreds of dead cats are found along the shore.

2. Book II: Psalms

The townspeople cannot determine the cause of death for cats found along the beach. Bev spreads rodenticide 1080 around the church to deter predators. Father Paul meets Leeza Scarborough, the mayor’s wheelchair-using daughter, who was paralyzed after local alcoholic Joe Collie accidentally shot her. During the annual Ash Wednesday "Crock Pot Luck" Festival, Joe’s dog dies after eating food from the ground, leading Joe to suspect Bev, whom he resents for persuading the townspeople to accept an oil company settlement that benefited the church. Erin, now a teacher, later sees a mysterious figure outside her home. Riley attends an AA meeting with Father Paul and condemns God over the fatal car crash he caused. That night, drug dealer Bowl is attacked by an unseen assailant. During Mass, Father Paul orders Leeza to stand and receive the Eucharist, and she miraculously walks.

3. Book III: Proverbs

Crockett Island experiences a religious revival after Leeza suddenly regains the use of her legs, which residents regard as a miracle. Leeza visits Joe and tells him she has forgiven him for causing the injury that left her paralyzed, prompting Joe to attend an AA meeting with Riley and Paul. Sheriff Hassan becomes concerned when he learns his son Ali has been studying the Bible, and later unsuccessfully argues against Bev distributing Bibles at the public school. Paul suddenly collapses, coughing blood before dying in front of Bev and the Scarboroughs, only to revive moments later.

In a flashback, Paul reveals that Monsignor Pruitt became lost in a sandstorm near Jerusalem and took refuge in an ancient ruin, where he was attacked by a winged humanoid creature that drank his blood before feeding him its own. Pruitt awoke restored to his youth, revealing that Father Paul is actually a rejuvenated Pruitt. Convinced the creature is an Angel, Pruitt believes its blood is a divine gift he intends to share with the island.

4. Book IV: Lamentations

Doctor Sarah Gunning discovers that Erin's fetus has vanished without explanation and concludes that she has miscarried. Distressed, Erin travels to the mainland for a second opinion, but another doctor finds no evidence that she was ever pregnant. After his resurrection, Paul learns that sunlight burns him, and Bev realizes he is Monsignor Pruitt. Unable to appear publicly during the day, Paul administers the Eucharist privately to Sarah’s elderly mother Mildred, who suffers from dementia but recognizes him as Pruitt. Joe later visits Paul and discovers him drinking the Angel’s blood, which Paul has been mixing with sacramental wine and distributing to the congregation.

Overcome by bloodlust, Paul kills Joe and drinks his blood. The next morning, Bev, Mayor Scarborough, and handyman Sturge find the body, but Bev conceals the killing, believing Paul’s resurrection signals the Second Coming of Christ. During an AA meeting, Paul falsely tells Riley that Joe is visiting his sister. Knowing Joe’s sister is dead, Riley returns to confront Paul and discovers the Angel filling a decanter with its blood before attacking him.

5. Book V: Gospel

Concerned by Riley’s disappearance, Erin files a missing persons report with Hassan, who suspects Riley may have relapsed or committed suicide. During Good Friday mass, Paul delivers a sermon urging the congregation to prepare for war as soldiers in God’s army, disturbing Mildred, whose health and memory have greatly improved through Paul’s visits. Later that night, Riley asks Erin to accompany him offshore in a rowboat. Once far from the island, Riley explains that after the Angel attacked him, he recovered under Paul’s care. Paul then revealed that he is Monsignor Pruitt and that he has been mixing the Angel’s blood into communion wine to heal the island’s residents.

Horrified, Riley left farewell letters for his family and Pruitt before visiting Erin. He explains that he brought her onto the water to protect others from himself and confesses his love for her. At sunrise, Riley bursts into flames and burns to ashes in front of Erin, who screams in horror.

6. Book VI: Acts of the Apostles

Erin returns to the island, where Sarah shows her Mildred’s restored youth and that her blood burns in sunlight, concluding that Paul has been causing apparent miracles through the communion wine and that Erin’s consumption of it caused her pregnancy to disappear. Erin tells Hassan, who refuses to investigate the church, fearing further stigma. Erin, Sarah, and Mildred try to flee but discover the ferries have been sent away. That night, Sturge cuts power to the town as Paul reveals he is Monsignor Pruitt and presents the Angel to the stunned congregation.

Explaining they have consumed the Angel’s blood, Pruitt urges them to drink poison and be reborn. Several parishioners comply, including Leeza’s parents, Sturge, Ooker, and Ali. Mildred shoots Pruitt before the Angel attacks her. The resurrected churchgoers then attack those who refused the poison. Erin shoots Bev, and she, Hassan, Leeza, Sarah, Warren, and Annie escape. Many slain residents, including Ed, also resurrect, while the revived Bev and Sturge unleash the undead congregation on the town.

7. Book VII: Revelation

Mildred reunites with Pruitt, with Sarah revealed to be their daughter; Pruitt admits he brought the Angel to the island to prevent Mildred's death and reunite their family. As the turned churchgoers massacre the town, survivors flee Erin’s burning house after Annie distracts Bev and Sturge by slitting her own throat. Erin, Sarah, and Hassan burn the boats to trap the turned on the island, while Bev orders all remaining buildings destroyed except the church and rec center, where the turned intend to shelter themselves. Horrified by the violence, Pruitt denounces Bev, who calls him a false prophet.

During the survivors’ attempt to destroy the final shelters, Sturge shoots Sarah, Bev mortally wounds Hassan, and the Angel attacks Erin. Erin cuts the Angel’s wings while it feeds on her, damaging its ability to fly. Pruitt fails to turn Sarah before burning the church, after which he and Mildred take Sarah’s body to a bridge she was fond of as a little girl. Ali destroys the rec center. With no shelter from sunrise, the remaining townspeople gather to die while singing " Nearer, My God, to Thee ". Leeza and Warren escape by canoe and watch the island burn as dawn arrives.

The wounded creature tries to fly away, but the story does not conclusively show whether it survives. Leeza tells Warren that she can no longer feel her legs: the healing effect of its blood is wearing off.