The Winx use Tecna's tech-savvy skills to find the Sirenix Book, but the Trix meddle with the Winx's search. When Tritannus learns of the Winx's mission to achieve Sirenix, he too, seeks to obtain it.
The Winx read the Sirenix book and discover they must first gain the power of Harmonix; meanwhile, Sky's blow to the head has erased his memory.
Continuing from the previous episode, Bloom despairs over what had transpired. Sky had been sent to the school's infirmary to tend to his injuries. The other girls try to lift her spirits, assuring that Sky will eventually regain his memories. Stella then provides everyone with new outfits, which Flora comments that she ought to become a fashion designer, where Stella gets psyched on the prospect.
Meanwhile, Icy reports to Tritannus of what had transpired, and he was angry that they did not finish off the Winx. Icy was quick to put the blame on Darcy and Stormy for "being too weak". Tritannus then tells Icy to do whatever she can to prevent the Winx from finding the Sirenix Book while he goes on his own search for the Sirenix power. Icy heads for Alfea again with Darcy and Stormy in tow, who were more than annoyed at how she portrayed them to Tritannus.
Back at Alfea, Bloom goes to visit Sky in the infirmary. While they are able to heal his physical wounds, they could not restore his memories. He gets a call from Erendor, which lead to an awkward conversation. Flora then comes in with Princess Krystal, telling that her healing powers will be able to do something for Sky. Once she tries, she was startled that she had come across a barrier, which prevented the healing process as well as a vision of the Pendant of Eraklyon. She tells Bloom that there might be something Sky is trying to forget, which is causing the barrier, but tells her to try and get him reacquainted with familiar sights to at least get some inkling back.
Tecna was in her room putting together a program sent by Timmy that would help her use her own phone to track the Sirenix Book. Unknown to her, the Trix were spying in stealth, and Darcy plants a spell upon the phone.
Outside, Bloom takes Sky out for a walk through a spot they usually go through. He still cannot remember anything about it, so she tries showing him photos. Again, this was met with little result. Sky despairs at not being able to even remember who he is, or the red-haired girl before him, and promptly excuses himself, leaving a saddened Bloom. She is then called back to the Secret Archives.
In the Archives, Tecna shows off her phone's newest feature, which will zero in on the Book of Sirenix. After activating it, they get a certain book, but once Bloom touched it, it shocked her with negative energies. She gets cautious and wonders if this book really is what they are looking for, but Tecna admonishes her, saying that her technology is flawless, and before anyone could stop her, she opens the book. She then gets cursed and turned into a robot, much to the horror of the other girls.
Underwater, Nereus and Ligea go to try and find Tritannus and reason with him. Unfortunately, they do encounter him and his mutant servants. They were shocked to see him now as a monster and he immediately attacks Nereus. Ligea begs him to stop, and then he makes her tell him all she knows about the Sirenix power. All Ligea could tell him was that it is an ancient power of Fairies that has not been attained for years, and the last known one to do so was Daphne. Tritannus,not satisfied with the answer, turns her and Nereus into his mutant servants. Phylla observes this in shock and hurries back to the kingdom.
Back in the archives, the Winx girls were shocked at Tecna's sudden transformation. Robo-Tecna then goes about to "initiate her programming", which is finding the Sirenix Book. All she winds up doing was making a complete mess of the place. The others transform to Believix to try and undo the curse the book made on her, but were confused when convergence did not do anything, as they soon discovered that the book was not the culprit.
Aisha then discovered that the phone attached to Robo-Tecna's chest was the thing responsible for the curse. They quickly try to get it off of her, but the robot proved to be too fast. After opening elemental books, which unleashed wind, ice, and water, the girls finally were able to remove the phone from Robo-Tecna's chest, completely undoing the robot curse and reverting her back to normal. Tecna was shocked over the mess she had made, and now it will be even more difficult to locate the book. Bloom tells Tecna to try using her phone again now that the dark magic on it has been dispelled. She does, and now they found the Book of Sirenix. However, Bloom is reluctant to open it. She informs the others that once they have opened this book, there is no turning back. Tritannus then tells the Trix their next course of action: tracking down Daphne.
- Flora asks Krystal to use her healing powers to help Sky to regain his lost memory, but in vain there is a barrier in Sky's head which is preventing her from doing so.
- The barrier seems to be the lost Pendant of Eraklyon.
- Timmy gives Tecna codes through their phones, helping them find the Sirenix Book, but Darcy curses the phone.
- Tritannus turns Nereus and Ligea into mutants.
- Tecna opens a book which her cursed phone found, and is cast under a spell by the book which turns her into a robot. Powered by the phone, she opens different books in her search for the Sirenix Book which causes much trouble for the Winx.
- Aisha notices the phone attached to Tecna and says that the cursed phone is the problem, and the Winx opened elemental books, which unleashed wind, ice, and water to knock her unconscious, then Bloom shot a Fire Arrow successfully at the phone to finally knock the phone clean off of Robot-Tecna's chest, completely breaking the robot curse and returning her back to normal.
- Tecna, then finally uncursed and healed, uses her phone again, now that the dark magic on it has been dispelled, to find the true Sirenix book at last.
- The Winx find the book due to Tecna's technological-based magic, but Bloom tells them that when they open the book, they are putting their very lives and whole entire beings at risk. The Winx Club must decide now, whether they are indeed ready for such a dangerous risk.
- Tritannus plans to hunt for Daphne.
- Darcy and Stormy begin to get very resentful of Icy, even more than usual since they joined Tritannus.
- Winx Club
- Alfea Students
- Believix Convergence - Used by the Winx to break Darcy's spell.
- Dragon Wing - Used by Bloom to defend Stella from Robot Tecna's laser attack.
- Morphix Wave - Used by Aisha to close the snow book.
- Fire Arrow - Used by Bloom to remove robot Tecna's cellphone.
- This episode is called "Tecna the Robot" on the Nickelodeon website.
- This episode was reuploaded onto Nickelodeon's website and is now called "The Sirenix Book".
- This is the third time a member of the Winx has fought with the other Winx members. This time was Tecna. The first being Bloom, as Dark Bloom in Season 2 and the second being Aisha in Season 4 after she lost Nabu.
- This episodes correct production code is 504, making stand-alone episode "The Lilo", next.
- Krystal is brought in to heal Sky, even though Flora and Bloom both have healing powers, as Flora healed the Tree of Life in Season 2 and the fairy pets in Season 4, and Bloom healed Sky in Season 2.
- When stopping to catch their breath after failing to catch Robot Tecna, Musa's wings are angled weirdly and they cut through her hair.
- In one scene, Stella's eye shadow in her Believix is baby blue instead of pale yellow.
- When Tecna opens the cursed book, her phone is to her right. When she turns into a robot and the phone binds with her, it levitates from her left.
- When Aisha tries to close the Snow Book, the book's cover is blue instead of light blue.
“Oh, Tecna, too technical.”
“We have found the Sirenix Book, and if we open it, our quest will begin. It will mean risking everything we have, everything we are. Are we sure we want to do this?”
“I never thought opening a book could be such a DISASTER!”