In a hospital room inside the convent, a police officer named Hugo and his wife welcome their newborn son. A nun named Anne-Marie comes in with "contraband" candy for the woman, then leaves.
Anne Marie, in the chapel, thinks she hears something and is so distracted that she almost bumps into another nun, Sister Louisa, and screams.
Hugo's wife asks him to get her a drink, and while he's gone, she's attacked and killed by a cloaked, clawed creature who takes the baby.
Cut to Zed listening to music; she's distracted, engulfed in drawing Old Testament images that came from the mind of Imogen when she touched the fallen angel. Among them, though, is an image of an Invunche, a twisted demon with no eyes which Constantine says is extinct.
Constantine leaves and Zed turns to find a woman standing in the mill house in white. When Zed calls John to pick up what he assumes is a girl he's sleeping with, he comes, and deduces that it's actually an astral projection. It's Anne-Marie. She says she needs him, that he owes her, and explains what happened to Hugo's wife.
She vanishes, and Constantine tells Zed that Anne-Marie must be desperate to come to him. We see the clawed creature lock up the baby.
Zed wants to come, but Constantine tells her to stay, not to leave the safety of the mill house, and to recover from her encounter with Imogen. She protests, saying that her knowledge of Spanish could be useful in Mexico, where he's going, but he dismisses her. Anne-Marie is from the Newcastle Crew and Constantine wants to handle this in private.
Chas arrives and the pair drive to Mexico together, arriving at the convent where they're surprised to see Anne-Marie is now a nun. Constantine flirts with her anyway, and she rebuffs him.
At the mill house, Zed is drawing when she starts to see and hear things, and gets up to look around.
At the convent, Constantine visits the scene of the attack and finds a "mouse" hole he says is probably where the spirit came from. He sets up to use rune stones to find the spirit.
Zed, meanwhile, has found her way around the mill house, including a door that leads to nowhere; opening it, you see the exterior of a building, but below that...emptiness.
Sister Louisa comes to summon Anne-Marie, who says she'll be along in a minute; Constantine performs his incantation and the stones catch fire. Constantine says it's actually a good sign; that simple baby snatchers/eaters wouldn't go so far out of their way to cover tracks. He says the baby is likely still alive and they need to find a link to it. Anne-Marie suggests digging up the placenta, which is buried in the parents' backyard for luck.
They arrive at Hugo's house, and Anne-Marie continues to give Constantine the silent treatment. Besides Newcastle, she's upset that before the seance, he had slept around just hours after their first time together. He apologizes, but she says his ego is out of control. He find a bear in the tree above where she's digging for the placenta, and it appears to be made of skin. It bleeds when he cuts it and the tree from which they picked it starts raining down blood. He says he knows who took the baby: One of Eve's sisters.
Inside, they tell this to Hugo, who says he feels helpless. Before they can fully process what's going on, Hugo gets a call: there's been another baby-snatching.
Zed goes to the art shop and model Eddie finds her, saying he was there for supplies. The two go for drinks. They're flirting and laughing but when she touches his hand, she realizes that he's keeping secrets.
At the scene of the second attack, the mother didn't see the baby-snatcher and so survived. As Hugo is trying to take her statement, his son arrives to say it was his baby and that's his girlfriend. Constantine, even without Spanish. figures out what all the yelling is about and susses out that the spirit is, for some reason, after Hugo's bloodline.
Constantine wants to summon the "hell goddess" responsible for he kidnappings to get a look and see which of Eve's sisters it is. Anne-Marie objects, and Constantine yells at her. Chas goes to console her while Constantine begins his incantation at the nunnery's fountain.
Chas tells Anne-Marie that it's because of Constantine's relationship with her that he now shuns most relationships -- that he can't do what he has to do if people are close to him.
Constantine starts to summon the entity but Sister Louisa comes to demand he talk to Mother Superior. When he dawdles, she becomes insistent and he figures out it's her. He rattles off the names of Eve's sisters until he gets to Lamashtu, and she tackles him into the fountain. She almost drowns him before he stabs her and she flees.
Zed brings Eddie to the mill house, where she incapacitates him. He says her father wants her to come home, and calls her Mary. She punches him.
Back in Mexico, Team Constantine goes to see Hugo's mother, who says her grandfather was part of an ancient race called La Brujería, and that her father had fled from him with the family. They were powerful warlocks from ancient Chile, who haven't been seen or heard from for thousands of years, says Constantine. He first won't believe her and then realizes that it's their return that's causing the Rising Darkness.
Constantine decides that they'll fill a chicken with Hugo's blood and then, casting a spell to make it look like a baby, con Lamashtu into taking it back to her hiding place.
After trying to sweet-talk Anne-Marie into being the one to deliver the baby, she sees through it, and offers anyway when Constantine tells her that they have to do anything to save the innocent.
Back at the Mill House, a man and a woman show up to back up Eddie, saying they're from The Crudsade. They kill Eddie when Zed tries to use him a sa bargaining chip and the man produces a syringe, saying she can come with them awake or asleep.
Anne-Marie and John discuss their "sins," Anne-Marie's being that she introduced Constantine to magic in the first place and he's her failure. He gives her the icon of Puzuzu, Lamashtu's former soulmate, to keep her safe and kisses her good-bye. She kisses him back, passionately, and then pushes him away. She summons Lamashtu and the deception works, but Hugo tears after the demon with his gun, blowing their cover. They convince him to stay up top, with Anne-Marie taking the gun, as Constantine, Anne-Marie and Chas follow Lamashtu into a sewer below the nunnery.
Zed evades her pursuers into the basement of the mill house, where the woman nearly catches her but Zed pushes her out the door into void.
The trio split up in the sewer but Constantine and Anne-Marie reconvene when they hear Lamashtu screeching, have discovered their deception. They find the babies and free them but Lamashtu catches them. Constantine refuses to surrender the baby to her, instead demanding to know her plan or he'll kill it. Lamashtu says la Brujería plan to tear down the boundaries between Hell and Earth and force mankind into hiding. She says he doesn't have the power to stop her, so Constantine summons Puzuzu, and Lamashtu burns up.
Back in the mill house, Zed is knocked out by the man who killed Eddie's syringe.
In the sewer, Constantine and Anne-Marie hear another baby but it's actually an invunche given life in the form of the blood-filled chicken. Constantine has no plan to combat or escape the creature, so Anne-Marie shoots him, saying that no cost is too high to save the innocent babies, and leaves him there to attract the creature while she escapes.