This year's Christmas exhibition in the department store is to be opened and Cecilie has been given the task. During the opening, Petra is asked about Absalon's secret, but she dismisses the questioner, but Cecilie thinks Absalon's secret sounds exciting. During the opening, a mysterious boy also appears, but quickly disappears again. Amir is worried because things are disappearing from the department store, but dad doesn't think it's a problem.

Cecilie sees the boy again and he runs away but knocks over a stack of cans on the road. Petra talks about Absalon and his time while Cecilie has a flashback to the same time period. Both Niels and Benedikte are stressed about buying gifts and Benedikte thinks the parents should stop giving each other gifts. Cecilie wants to go to the ruin but Amir stops her and when she meets the boy again she promises not to reveal him.

Cecilie has heard a secret about the dungeon and gets help from Hubert to get into the basement. When they are standing at the entrance to the ruin, they still don't dare go in. Hubert also soon gets scolded by Frode because Cecilie is in the basement. Up in her room, Cecilie makes a map of the basement and talks to Ida about the project.

Mother talks seriously with Cecilie and Ida about the ruin and when mother has to go to a meeting she asks Cecilie to look after Ida. Ida goes into the basement and down into the ruin so when Cecilie discovers it, she sets out after Ida with help from Hubert. At the last moment they find Ida who is very ill again. This makes Cecilie pack up all her archaeological things and declare that she does not want to be an archaeologist anymore.

Hubert believes the secret can make Ida well because she is an angel. He knows this from a letter Frode has and Cecilie seeks out the three in the basement for help. But Frode only has part of the old letter from Margrete the first. Meanwhile, Amir gets more people to help solve the many thefts from the department store.

Cecilie 'borrows' her father's key to the exhibition so that she and Hubert can get to Absalon's stav. Here they find the second part of Margrete's letter. Down at Frode and Ib's, the four of them read the letter and discover that the children are going to Roskilde Cathedral the next day. Meanwhile, Amir believes that the thefts are being committed by the store's own employees, but this is denied by Niels.

Cecilie skips school so she and Hubert can go to Roskilde Cathedral. Here they have to get hold of a key on display, and Hubert distracts the attention while Cecilie steals the key. This gets Hubert caught playing with the church choir, but soon the guard is after both children. In the meantime, Petra has discovered that the exhibition has been tampered with, and Hubert can't remember anything about his family, to Cecilie's surprise.

Father suggests they hire a maid and soon Lisbeth has taken over the house, but she has a lot of questions that mother soon gets tired of. Frode works on translating Margrete's letter but has to give up. Hubert accidentally spills water on the letter and when it is dry the letter can be read. Cecilie asks Petra for help and Petra wants to watch the surveillance tapes to find the thief, but Cecilie deletes the tape. That same evening Hubert joins in for dinner, but suddenly has to leave.

Petra and the computer expert are looking for the things Cecilie deleted from the surveillance tape. Cecilie lies to her parents again and takes Hubert to Kalundborg Church. Here the two help clean the church while desperately searching for a clue. On the way home, they go into Kollinus' shop and here Hubert finds a clue in the front of a letter from Margrete. At home, Petra has discovered who was in the exhibition and tampering with the objects.

Ib and Hubert steal the department store's Christmas tree without knowing Ida is going to turn on the lights that same day. The proceeds from a collection that same day are going to poor children so they deliver the tree back to Amir's great confusion. Cecilie and Hubert get ready for the next phase of the adventure and Hubert steals some tin figures from the toy department but it is Cecilie who is caught.

Father and mother discover Cecilie has been truanting and they forbid her from seeing Hubert again. But Hubert gets Cecilie out and together they go to Ringsted Church. Here Cecilie is discovered when she wants to make a copy of the key, but Hubert distracts attention and escapes over the church ceiling. Back home, Ib has a copy of the key made while Petra tells about the excavation. And Cecilie discovers the key is a map that shows the entrance to the dungeon.

Petra follows Cecilie down to the basement and meets Ib. She questions him and he answers her questions in a frightened manner, thereby revealing the plan. Cecilie and Hubert go down into the ruin and look for the well, and soon Cecilie is down there. But the water rises quickly and Hubert faints in the darkness. Up from the ruin, Petra lies about Hubert to Cecilie and Cecilie is very disappointed so she breaks off her friendship with Hubert.

Petra is down in the ruins when Cecilie comes along. Cecilie proudly tells them she has found the entrance to the dungeon and soon she and Petra are down in the well. When they are on their way back up, Petra steals the key from Cecilie.

Petra is alone in the dungeon but can't open the door any further in. Ib admits he has been gossiping to Petra so Cecilie and Hubert can become friends again. Frode and the children spy on Petra and find unknown glowing things in Petra's bag. As revenge, Petra gossips to Amir and Frode and Ib in the dungeon.

Dad and Ida are having a great Christmas but Amir interferes and wants to organize a cleaning of the basement. Ida warns Cecilie on her cell phone so she can warn the three in the basement. They clean the basement but now have to hide in the girls' room. Ib admits he is to blame for the mess, so Hubert and Cecilie spy on Petra again.

Frode and Ib sleep under Ida's bed and play with Ida the next day. Cecilie and Hubert plan to trick Petra, and follow her down to the basement where Petra has a secret room. When the two are locked in, they find an exit and at the same time another entrance to Frode, Ib & Hubert's old part of the basement. The two children manage to steal the key from Petra and escape.

The basement is cleaned up and a trap is laid for Petra. Cecilie and Hubert go down into the ruin and into the dungeon but are caught when some stones collapse. The two children crawl on and it turns out they have found a hidden and forgotten passage to Christiansborg. Mother wants to go away for Christmas but realizes it is impossible to get more than 1½ days together with the whole family.

Frode, Ib and Hubert must trick Petra into staying away from the ruin and they lock her in a basement room. Cecilie and Hubert find the dungeon and they go further into the ruin. Here Hubert gets sick and disappears so Cecilie has to look for the exit alone. Cecilie gets tired and doesn't see Margrete's spirit leading her to Hubert. Cecilie and Hubert don't make it out before the water is turned off, so they spend the night in the ruin and Hubert sleeps constantly.

Mom and Dad talk to a psychologist about their stressful lives. Cecilie and Hubert are still in the basement and text Frode for help. Cecilie and Hubert open the door to the angel and a flash of light flies through the air. Hubert is in a trance and has angel wings, while all the lights in the house are affected and everyone becomes happy. Hubert remembers nothing afterwards, but Petra and Amir have witnessed the entire session.

Petra contacts Edward and arranges the final details about Hubert's relocation. Cecilie has discovered that Hubert is the angel, but when he tries to cure the very sick Ida, he fails. So he goes into flight training, while Frode is sad about losing Hubert. Everyone has now found out that Hubert woke up in the ruins when the subway was being dug out, and Petra makes a plan to catch Hubert. It fails and Hubert asks Frode for help.

Frode searches through books about angels but finds nothing useful. Ida is now very ill and her parents do not leave her bed. Petra watches over Cecilie. Cecilie finds the solution to how Hubert can get the strength to heal, so when Margrete's bones are moved down into the ruin to Hans', Hubert lights up. As the two children are on their way up, Hubert is caught by Petra and Amir who have seen everything.

Cecilie, Frode and Ib look for Hubert and find him in Petra's workshop. When Amir discovers Frode and Ib's basement, he calls for help and the two are captured. However, Niels releases the two, and Amir is tired of it all so he tells Petra. But she gets him fired and in the meantime prepares Hubert to be sent to his English museum colleague.

Amir helps Cecilie save Hubert and the two trick Petra and Edward. With help from Frode and Ib, Petra and Edward are taken to the police with a whole box of Danish cattle Petra has stolen from the excavation.

Ida is now so bad she has to go to the hospital. Cecilie runs into the basement after Hubert and with Frode and Ib's help, they manage to get Ida up onto the roof. Here Hubert heals her, and then Hubert goes up into the sky. Soon the world is turned upside down: Ida and Cecilie are skating and Amir is the shift manager. On Christmas Eve, everyone meets in the basement at Frode and Ib's house, where they are having Christmas for the homeless.