To distract Elsa from a gala being planned in her honor, Anna fills her schedule with fun bonding activities. But what starts as a distraction turns into an adventure when they find a secret door leading to passageways within the castle walls—and the door locks behind them, trapping them inside! Then, as they explore the narrow passages and sealed-off rooms, looking for an exit, spooky things start to happen. Echoing laughter, mysterious patches of cold air, odd arrangements of clothes and furniture…what could be causing all these strange events?
With Elsa's powers and Anna's ingenuity on their side, they're more than a match for whatever they find—if they can just find it in time! Packed with humor and heart, Phantoms of Arendelle will keep readers guessing right up until the last page.
The story begins with Anna in the castle library flipping through the pages of a book on myths and legends around the world, one of her favourites when she was a little girl, when her sister was still hiding from the world. Back then, Anna had worked her way through nearly every book in the library and there wasn't much else to do. But now things were different, everything about life in the castle had changed since Elsa returned from the North Mountain and learned to control her powers. By Elsa royal decree, the gates were always open, sunlight screamed through the unshuttered windows, and villagers and guests came and went freely every day. For Anna it was a great change in life but sometimes found herself thinking about all the things her sister missed out on while she was locked away. Despite knowing Elsa now much happier, Anna couldn't help wonder if she could make her life even better. So she decided to come up with something that would properly welcome her sister back to the world of open doors, and thanks to a book on Phantoms found by Olaf, she knew just how to do it.
Elsa too was feeling the same way as Anna was, and was planning a surprise banquet in honour of her sister. While doing her paperwork a pig charged into her office with Anna in pursuit of it. All her attempts to catch it failed as the pig managed to evade her graps but with a wave of Elsa's hand, the temperature dropped instantly and a sparkling shimmer appeared around the confused animal which formed an icy fence. With the pig under control, Elsa turned to asking Anna why there was a pig in the castle. Anna told her about a story she found in the library about the boar that can transform into shows and thought it would be a fun idea to make this pig a boar. Elsa remembered that story but pointed out that what she had wasn't a boar, it was a round pink pig. Anna said they could teach it to be one but Elsa just gave her a skeptical look, and before either one of them could say anymore, the pig leapt over the top of the icy pigpen and ran out the door. Anna chased after it and so did Elsa, after realizing this distraction might just be the thing to keep Anna busy and avoid discovering her surprise banquet.
The chase led them losing the pig but left the two sisters lying in matching collapsed heaps on a grassy patch, covered in mud. Despite being all dirty, it was all part of Anna's plan. She wanted to give Elsa a surprise ball and to make sure she didn't find out about it, she had a whole afternoon of fun planned out for them so the staff could get things ready. They had a long fun adventure around the village till the evening came. They had a race on horseback, an archery competition, sampling every kind of cheese they could find and had a sleepover in the most comfortable bed in the nicest Inn. Elsa really enjoyed all these new things but then remembered that it was the day of the banquet. Knowing the staff was at the moment setting things up, Anna would find out if she went back to the castle. So she decided to keep her more occupied by continue on with the rest of the fun things they had yet to do together, like a pillow fight. With the pillow fight over, they went to the fjord and Elsa used her ice powers to make beautiful sculptures on the surface of the water. Anna suggested this in order to keep Elsa away from the castle a little longer, since she ordered a gigantic cake for her surprise ball and was being delivered as the Great Hall was being decorated. Then by nightfall, she could lead her sister back to the castle and surprise her with cake, decorations, music and laughter. It was a perfect way to end the day, but little did she know that Elsa too had a surprise for her as well.
After receiving a note from the court page, Elsa needed to hurry back to the castle because plans for her banquet had gone wrong. The bakers had run out of ingredients while taking care of other high-priorities, the custom streamers she ordered had somehow been mistakenly sold for some over event, and the musicians she hired were no longer available. This made her wonder why all this was happening. Not that it mattered, what was really important was to attend these issues while keeping her sister occupied which would be difficult, as Anna was following her every step of the way. In the hallways, Anna and Elsa came across a mirror that opened to a secret passage when Anna pushed it. Elsa remembered rumours about the castle being filled with twisty hallways and secret rooms all inside the walls but never believed they were true because it was said these hidden parts were haunted by ghosts. Just then Elsa heard a noise from further up the hallway. Rounding a corner she spotted twelve strong men with the huge cake Anna ordered. Mistaking it for the cake she ordered, Elsa made sure Anna didn't see it by deliberately shoved her inside passage and pulled the mirror almost completely closed behind her. She claimed that she tripped and just as Anna moved to the hidden door, there was a loud thump, and the door shut completely. Knowing they couldn't go back the way they came, they decided to venture further into the long forgotten hallways and find another way out, at the same time keep each other from seeing each other's surprises. The passages were haphazardly arranged, some clearly having been leftover space between the walls, and others having been purposefully constructed. They came across a lot of doorways, secret rooms and piles of creates that were filled with stuff that had been long forgotten. At the same time, they discovered strange footprints and heard noises. Anna suspected it to be ghosts but little did they know that it was actually Olaf who had somehow found himself in the passageways and was looking around for Phantoms.
Soon Anna and Elsa felt like they had been walking for miles and there was no end to these passages. They suddenly found themselves in an old storage room full of racks and boxes of clothes, mostly old dresses that were out of fashion. Anna began to feel they would never find a way out or get to Elsa's surprise ball in time. She sadly crouched down next to one of the uniforms and Elsa sat down beside her. Anna felt because Elsa was Queen she was now very busy running kingdom and she wanted her to be happy and do so many things with her. Elsa tells her she already is happy but admits being Queen is still all new to her and is trying to be as good as their parents were. Anna tells Elsa she is doing well with being Queen and after their parents were gone, she has been trying her best to be there for her. Elsa put an arm round her sister and told her they were not gone as long as they remembered them and had each other.
Suddenly they were interrupted by a nearby screech, clearly being made by Olaf who was moaning and howling in hopes that if he acted like a phantom, he could get them to come out. Anna and Elsa ran after the sound of where it was coming from. They climbed up a pair of rickety stars that didn't look safe and could give way anytime. Suddenly the staircase began to fall apart from the basement up. They ran up as the staircase collapsed behind them till finally they safely reached a small landing jutting out of the castle wall near the very top. It extended for only a handful of feet, and from there, another rickety staircase descended only for both staircases to crumble down at the same time. Anna and Elsa were now preciously perched on a five foot long, three foot wide stone ledge and to their horror, they spotted a small, sheet-draped spectre of some find which they considered to be the phantom they had been following. Then they heard a loud bong of ringing bells which was the clock tower. Suddenly both Anna and Elsa remembered out loud that it was now seven o'clock, by the slip of their tongues mentioned their parties which ended in in a short pause. Remembering the Phantom, Anna decided it was time to capture it and get out of the castle walls once and for all. With that, Elsa created a giant ice slide, starting at their feet and plunging into the darkness towards the ghostly figure. Then with a grin, Elsa shoved Anna onto the slide and jumped down after her. They crashed into the ghostly figure and swept him away as they continued to hurtle into the dark. Suddenly a dead end loomed out of the darkness. Elsa created a huge cushion of snow and the three of them crashed directly through the snowbank and found themselves in the Great Hall where they crashed into the cake that Anna ordered. Both sisters sat up covered in cake, then after looking at their surroundings, yelled at each other, “Surprise!” which led to confusion between the two. After discovering the Phantom was in fact Olaf, both sisters realize they were both planning surprise events for each at the same time and decided to combine their ball and banquet into one ultimate gala.