Valtor and Obscurum intend to attack a new star, Syderia, and to do so, they decided to adopt a different strategy: deception. When the Winx come to the rescue of Syderia, they discover that the Lumens that inhabit it are convinced that the fairies came to steal the treasure of their star. After discovering that in the subsoil of Syderia there is a mountain of crystal, the Winx make it shine with their Cosmix powers. Bloom has the idea of bringing a crystal fragment to Orion to make him build new core for the dying stars.
In Valtor's Palace, Valtor summons Obscurum, warning him of his final chance to get into his good graces, questioning about his plan to attack Syderia. Obscurum attempts to formulate a plan on the spot after being side-eyed by Valtor who quickly grows impatient of his incompetence, sending him into the trap dimension once again. Valtor grants him more time to formulate a plan.
At Alfea, Stella asks the girls for their opinion on the better looking earrings, to which Aisha responds by questioning the relevance of their responses, citing how Stella tends to go against their advice regardless. Musa tells Stella to ignore this response, and reassures her of her beauty regardless of what she chooses. Flora is distracted by her previous disagreement with Helia, wondering how she should break the tension between them when Tecna reaches out to her. Bloom reassures her that her disagreements are ordinary for a couple, with Stella backing her up, going on an analogy about her earrings, though receiving a tad ire from her friends for the far-fetched characteristics of such. Flora continues to get reassured by Bloom as Stella obtains a message from Brandon about a new winter hat he gotten, to which Stella uses it as an example of disagreements between couples as she blasts the hat's style. Tecna sends Timmy an emojix though Aisha tells her that face-to-face conversations are the most effective and repairing the cracks in their relationship which Flora seems to resonate with the most. Stella talks about her smooth-sailing relation with Brandon, which inspires Flora to send Helia a message.
At Red Fountain, Helia notices a rose suddenly coming into bloom, letting him know that Flora is thinking of him. Back at Alfea, Flora gets ready to meet Helia when she receives a text of acknowledgement from him. She is elated to receive it and as she is about to leave, Twinkly asks her for help to set up the party decorations. Flora tells her about the meet up she has with Helia, to which Twinkly replies for her to hurry so she can help as Kiko and Knut show up to assist though end up causing a ruckus. Flora ends up crashing into Helia and quickly reconcile.
On Syderia, Obscurum and the Staryummies arrive. the Staryummies begin to take in the light of Syderia on Obscurum's command as he prepares for his victory. The star gets darker, causing the Lumens to get fatigued as they begin to fall asleep. Obscurum enchants the Lumens with a nursery rhyme about the Winx being greedy creatures who would steal their treasures.
At Alfea, Knut, Kiko and Twinkly continue setting up the party as the Winx prepare for their concert, though Twinkly becomes aware of the attack on Syderia, and gets the Winx to leave after granting them their space travel suits. Knut and Kiko get strung along by Twinkly to assist the fairies after granting them their own space travel outfits. The Winx arrive on Syderia, much to the Syderian Lumens' dismay, to which they plan to mount a defense to stop their plans. The girls arrive at the core, noting how it is obviously still in good health with no signs of aggravation. The girls transform to more closely examine the core, but get confronted by the angry Syderian Lumens who chase them down, repeating the rhyme they were fed by Obscurum.
Kiko and Knut follow Twinkly to Syderia, though land further away from the core than expected and proceed back. Obscurum continues to absorb the magic energy of the core with the aid of the Staryummies after the Lumens and Winx have cleared out. Once the last spec of core energy has been taken, the star goes dark and a protective barrier forms around the city of Lumens. The Staryummies retreat and Obscurum destroys the core. The trio find themselves at the core just short of the attack, finding it to have been destroyed, much to their dismay and confusion at the lack of the presence of the Winx.
The Lumens realise the core has gone out and blame the Winx. The girls attempt to stop them and examine them to understand the reason for their aggression, realising that Obscurum likely played a role in this. The separated girls rendezvous with each other to cook up a new plan to escape their fury, finding out about the magic barrier surrounding the civilization much to the fairies' dismay. They retreat into a crack in the ground, finding the trio, learning about the destroyed core. They enquire about the rhyme reiterated by the lumens, finding out about the history of it. The Lumens arrive though Knut manages to halt and entertain them through their shared sense of humour though their ogre characteristics partly at Kiko's expense though un-cooperation.
The Winx plan to find the treasure of Syderia to earn the Lumens' trust. They quickly find it due to its strong magic glow and power it further to light up the star once again. The sleeping Lumens awaken. Kiko and Knut get bound by the angry Lumens after failing to conintue to entertain them but immediately drop everything when they see the glow of the crystal, elated to find the once hidden treasure, realising that the Winx are not their adversaries after a simple explanation of their misunderstandings. To thank the Winx for saving their star, they offer a small piece of the crystal. Bloom thinks to get Orion to use the crystal to build artificial cores for other broken stars which excited the other Winx
Obscurum details his plan to Valtor, labelling it as a success before asking for a reward, which angers Valtor as he shows how his plan has plainly failed who wants to send him back into the trap dimension, but has a new revelation to solve his issues by targeting Bloom whom he sees as the bane of his existence, causing all of his issues, and instead chooses to get Obscurum to conquer Lumenia immediately, shutting down his cheers.
- After their previous argument, Flora and Helia reconcile.
- Using a different strategy, Obscurum uses the Syderian legend to make the Syderia Lumens turn against the Winx.
- Discovering that Syderia is in danger, the Winx and Twinkly along with Knut and Kiko heads to Syderia.
- Under Obscurum's spell, the Syderia Lumens assume the Winx as their enemies and chases after them.
- Meanwhile, Obscurum steals the light from Syderian core and destroys it.
- Thanks to Knut and Kiko's distraction, the Winx find the treasures of Syderia and decided to light it up with their Cosmix powers to prove to the Lumens that they are not their enemy.
- After clearing the misunderstanding, Bloom asks for a fragment of Syderian crystal in order to have Orion to make artificial cores to light up the dying stars.
- To defeat the Winx once and for all, Valtor decides to target Bloom for his next plan.
- Cosmix Analysis - Used by Tecna to analyze the Syderia Lumens.
- This marks the last Cosmix transformation for the first half of Season 8.
- Flora sending a message to Helia by using a flower is a reference to Season 2, where she previously did the same thing in the aforementioned season.
- In one scene, Stella's wings have a green aura.
- In one scene, Flora's headpiece is layered under her hair.
- In one scene, Tecna's hair accessories are misaligned with her head
- In on scene, Stella has two stars on her belt.
- Bloom's hair piece vanishes in one scene.
- In another scene, it is layered under her ponytail
- The gem on Knut's belt changes opacity between scenes
- In one scene, there are black outlines on the highlights of the gem as well.