On many a dark night people would see her walking along the riverbank and crying for her children.
Luis Alvarez and his son Rafael go to the river to fish. As they set their hooks, they see a woman in white walking along the riverbank, crying. She walks into the water and Luis assumes that she's committing suicide. He dives in the water to rescue her but finds no trace of the woman. When he comes up, he sees the woman on shore, leading Rafael away. Luis runs after them but by the time he follows them to the road, they've disappeared.
Nick picks up a flail from Marie's collection at the trailer and takes it to Monroe. He has overdecorated his entire house for Halloween and tells Nick that Halloween is the Wesen's favorite time of the year. Monroe sets up the flail as part of a pumpkin-smashing dummy and demonstrates it for his friend. As they talk, the station calls to tell Nick about Rafael's disappearance and the detective takes off after making Monroe promise not to hurt anyone.
Detective Valentina Espinosa has a nightmare of the woman in the white dress, lying beneath the water and screaming. Valentina looks at her investigation board and the articles about missing children throughout the U.S.
Nick and Hank drive to the river where Wu is trying to question Luis. Neither one of them speaks the other's language and the translator is out of town. Wu explains that Rafael was abducted and that some kayakers got footage of the abductor. They view the woman on the tape and Rafael going past, and Nick calls Juliette and asks her to fill in as translator for the police.
Back at the station, Hank and Nick report to Renard while Ryan the intern comes in to the office and tells them that Juliette is there. Ryan ushers her in and she and Renard stare at each other for a moment. Nick and Hank then take her to see Luis. She tells them that Luis went to help the woman and then she left with his son. He has no idea who the woman is and his own wife is dead. The detectives decide to take Luis home and see if they can find anything at their home and Juliette goes with them.
As Valentina goes over her files, she gets an alert about Rafael's disappearance. Angry, she briefly transforms into her Balam jaguar form and then books a flight to Portland.
Hank, Nick, and Juliette take Luis home and discover that his neighborhood is celebrating the Day of the Dead with huge amounts of decorations. They don't find anything useful except a family photo that they can use to get a photo of Rafael. The neighbors offer their condolences and one woman, Pilar, seems intrigued by Juliette. She talks to Juliette, who explains that her mother grew up in Spain and taught her the language. Pilar then tells Hank and Nick that she knows who took Rafael. Luis snaps at her, saying she isn't helping, but Pilar describes the legend of La Llorona, the ghost of a crying dead woman who steals children. Pilar tells them that La Llorona took Rafael and when they show her the video, she claims that the ghost matches the woman's description. Wu takes the photo of Rafael and starts canvassing the area while Hank assigns an officer to stay with Luis in case anyone contacts him.
As the detectives leave, Pilar see the cat scratches on Juliette's hand and says that she knows that Juliette was sick and can't remember how she was scratched. Juliette refuses to talk about but Pilar insists that she face the truth. Nick asks Juliette if she can stay with Luis as a translator and she agrees. However, she avoids telling him what Pilar said.
At the station, Renard is talking to one of his people trying to determine why another of his people, Duvall, was tortured to death and whether he gave up any names. Ryan knocks at the door and tells the captain that Valentina, a police detective from New Mexico, has arrived with information about the abduction. The intern brings her in and Valentina offers to help, claiming she has vital information about Rafael's abduction. Renard introduces her to Nick and Hank and she warns them that there will be two more abductions before midnight. The unsub, the woman in white, has struck in dozens of other cities that she knows of, and Valentina warns them that the unsub will kill Rafael and her other two victims by the next morning if they don't find them.
At a cabin near the river, La Llorona kneels next to Rafael and soothes him. He stares calmly up at her as she transforms into a hag.
Trick-or-treaters arrive at Monroe's house and he gives them candy. As they go, three bullies take the candy from one of the girls. Monroe tells them to give it back and when they refuse, he grabs the ringleader and forces him to give it back. The kid and his two friends promise that Monroe will be sorry and leave.
Valentina describes how the woman in white always abducts two boys and a girl on Halloween Eve and then drowns them. She shows the detectives a sketch based on an eyewitness' testimony and they confirm it matches the woman in the video. As Valentina watches the video, she briefly loses control and Nick sees her true face. She then says that the children are always taken where near two rivers meet, in a triangular pattern. In each case with a witness, they saw the woman crying and thought she was trying to call herself. As Franco calls Renard away to check some files, Nick asks Valentina about the legend of La Llorona. Valentina has heard of the stories, which feature a woman who drowns her children as revenge on her husband for leaving him. However, the detective insists that it's just a legend and that their killer is real.
Renard goes to his office and tells Franco to run a background check on Valentina. He then reviews a private report showing that Adalind recently flew to Vienna... where Renard's brother Eric lives.
The parents take their children into the forest to celebrate Halloween. One of the children, Kalli, wanders away and sees La Llorona crying on the riverbank. She asks if the woman is okay and La Llorona comes over and takes her hand.
Valentina, Nick, and Hank try to pinpoint where La Llorona will strike next. Renard informs them that they've received a report of another child abduction near water. The detectives call Wu and bring him up to speed, and he tells her so she can translate for Luis. Pilar comes in with a gift of food and Luis angrily tells her that she's not helping. He storms out and Pilar tells Juliette that she has to work out what she does understand what she doesn't. The Spanish woman warns Juliette that her world is coming apart and that she will have to choose between two that she feels for. Juliette angrily tells her that she isn't choosing between anyone.
Hank, Nick, and Valentina go to the new abduction scene and the officer on the scene tells them that there was a witness. They go back to talk to the witness but Renard arrives and informs them that she checked New Mexico and confirmed that Valentina was relieved of duty three years ago. She insists that it isn't important but Renard tells them that the FBI want her charged with impersonating an officer and that they'll be taking over the investigation. He tells the officers to bring her in and leaves, and Valentina starts to lose control. Nick restrains her and warns her not to something she'll regret. The Balam figures that Nick wants to kill her but he says that right now all he wants to do is stop La Llorona. However, he warns her that he'll shoot her if she puts up a fight.
La Llorona takes Kalli to the cabin and has her lie down next to Rafael.
Back at the station, Renard interrogates Valentina, pointing out that she was fired from the New Mexico police because she was obsessed with the abduction. Valentina explains that she was watching her sister's child five years ago and La Llorona took him. She saw the unsub and warns La Llorona will claim her third victim and kill all three children at midnight. However, Renard tells her that she'll be staying in custody until the FBI can speak to her.
That night, the three bullies lurk outside of Monroe's house and plan their revenge.
Nick and Hank figure that Valentina is right and go to the trailer to see if they can find anything on La Llorona. One of Nick's ancestors left an entry saying that he saw a creature called La Llorona in Veracruz in 1519. It followed the same pattern of abductions, and the journal shows a symbol that matches the pattern of abductions that Valentina described. According to the journal, La Llorona isn't a Wesen but something else. When the Grimm set out to kill it, he never returned. The partners figure that the FBI can't handle the situation and head back to the station.
The three bullies break Monroe's front window and run away.
Nick and Hank release Valentina and tell her that they believe that La Llorona is real. They take her with them and head for the third point of the triangle matching the symbol. However, as they get to their car they receive a radio report that a Tino Diez has disappeared along the river in the area they were heading for. The detectives work out that La Llorona will kill the children at midnight at the spot where the two rivers meet. They have only fifteen minutes left to get there.
La Llorona takes her victims to the riverbank and calls out, asking that her children be returned. The spirits of her three children rise out of the river and La Llorona offers to sacrifice her three victims to bring them back for a year. Nick, Hank, and Valentina arrive and the ghosts retreat. While Hank and Valentina pull the three children away, Nick tackles La Llorona, knocking her into the water. They struggle and the creature reverts to its hag form. It starts to drown Nick but suddenly becomes human again. It sinks down into the waters and disappears. Nick swims back to shore and Valentina points out that midnight has just passed.
The trio takes the children back to the station and they are reunited with their parents. Juliette has brought Luis there and smiles as Luis hugs Rafael. Ryan congratulates Nick and then the detectives wonder if La Llorona really was a ghost. They figure that they'll have to wait another year to find out. Renard tells them that the FBI has arrived but the detectives point out that they couldn't have solved the case without Valentina's help. The captain agrees to let the FBI take the credit if they'll drop the charges against Valentina. Meanwhile, Juliette looks at Nick and remembers telling Pilar that she wouldn't choose anybody.
The three bullies hide near Monroe's house and watch the video they took of their breaking Monroe's window. As they plan to put it up on YouTube, Monroe finds them and takes away the camera. He says that they'll get it back when they pay for the window, but the bullies say that they're not frightened of him. At that, Monroe turns into his Blutbad form and they run away in terror.