A new day begins as Rapunzel reflects on all her adventures and paints a mural, while a shadowed figure makes its way through the forest neighboring Corona, revealed to be Cassandra. Meanwhile, Eugene is debating with himself on whether or not to propose to Rapunzel and decides to ask advice from Mrs. Crowley, who gets the wrong idea about him.
In the Palace's party hall, Rapunzel has gotten most of her and Eugene's friends together to plan a surprise birthday party for him, but is having trouble keeping him from discovering the surprise, so she sends Lance Strongbow to keep Eugene distracted while she finishes the preparations. Rapunzel's parents, as well as King Edmund, assure her that everything will be okay, and she heads back to her room for her surprise birthday gift for her beloved. Once they are alone in her room, she reveals to Pascal that she plans to propose to Eugene before he blows out his birthday candles.
It is evening by the time Eugene and Lance return to the castle, and Pascal informs Lance to keep Eugene stalled for a few more moments, and then gives him the all-clear two seconds later. Once Lance pushes Eugene through the door, Eugene is overwhelmed with Rapunzel and their friends surprising him with the planned party. He is indeed surprised, especially when the cake is brought out, and everyone reveals that he is twenty-six years old when he himself thought he was twenty-five. Just as Eugene is about to blow out his candles, Cassandra enters the room, crashing the party. Rapunzel hopes to make amends with her former best friend, but Cassandra has other things on her mind: She came for the Graphtic Scroll, but Eugene tells Rapunzel not to hand it over to Cassandra, who mocks her former friend over her ability to make decisions. She leaves after telling Rapunzel that she'll give her time to decide on whether or not to give up the scroll.
Inside Rapunzel's room, Rapunzel, Eugene, and the gang convene on how to handle the situation. Eugene suggests hiding the scroll, but there's a problem. Rapunzel doesn't have the scroll; Varian has it, so they head to the Demanitus Chamber, where he has moved his laboratory. Varian reveals that, in addition to the Healing and Decay Incantations, there is a third incantation, one that can allow whoever holds the Moonstone Opal to control the Black Rocks, and there is also a fourth incantation, but he has not found it anywhere on the scroll, just as Cassandra enters the laboratory.
Rapunzel orders Varian to hide the scroll so Cassandra cannot get her hands on it, but he reveals that the Translation Key is needed to even read the scroll. Eugene tries to cover Rapunzel and Varian, but in attacking Cassandra, he realizes that her armor is made of the near-indestructible Black Rocks, and is knocked back down the stairs. Cassandra cuts off one of the giant orbs that decorates the Demanitus Chamber, resulting in Maximus and Eugene dangling off a ledge and Lance attempting to pull them back up.
Cassandra battles with Rapunzel, who tries to talk some sense into her, and Cassandra reminds Rapunzel again of what she saw in the House of Yesterday's Tomorrow. Rapunzel tries to remind Cassandra that Gothel kidnapped her and held her against her will, while Cassandra reminds Rapunzel of how Gothel was pushed out of a window to her death. Rapunzel tries to explain what actually happened, just as Ruddiger suddenly attacks Cassandra and escapes with the scroll. Cassandra chases after him but is tripped up by Rapunzel's hair, while Pascal reaches the scroll first and escapes with Ruddiger. After a few moments, Rapunzel snags the scroll away from Cassandra and tries to reason with her former friend once more, and her words seem to reach Cassandra, until the Enchanted Girl reveals herself and tells her not to doubt the path she has now gone down. The odd thing is, only Cassandra can see or hear the Enchanted Girl. When Rapunzel says she won't fight Cassandra, Cassandra cements the fact that she is now Rapunzel's enemy by bringing down the Demanitus Device with her Shadow Blade, causing a chain reaction that destroys the entire chamber.
Rapunzel is barely able to hold the downed apparatus away from Maximus, Lance, and Eugene to prevent it from crushing them, but as she is focused on helping them, Cassandra steals the scroll with ease and goes after Varian, who destroys the translation key to prevent her from deciphering the scroll's contents. Unfortunately, she ends up kidnapping him when he explains that he has memorized the incantations and the Translation Key, while our heroes narrowly escape with their lives.
Cassandra returns to the forest with Varian as a captive, and the Enchanted Girl, watching from up close, reminds her that defeat is not an option, now that they have the scroll. She also informs Cassandra that Rapunzel will come for Varian to rescue him, which gives Cassandra the idea of building a stronghold, and she also has the idea of where that stronghold should be: the former location of Rapunzel's Tower.
Once Cassandra arrives at that location, she binds Varian to one of the Black Rocks, and as he stirs himself awake, she demands of him the third incantation on the Graphtic Scroll, but he refuses, and she reveals that she found his truth serum and forced him to drink it (since he sleeps with his mouth open). Now under the effects of his own serum, he reveals the incantation to control the Black Rocks, which Cassandra uses to build her own tower and stronghold.
In Rapunzel's bedroom, Rapunzel reconvenes with her friends to find out what Cassandra plans to do with Varian and the stolen scroll, but the others are not as optimistic as she is, as Cassandra broke their spirits very much. Rapunzel convinces them to help her go after Cassandra, as she was once their friend, but Eugene notes that they don't know where Cassandra is, until Maximus reveals the tower outside in the forest near Corona.
Cassandra brings Varian up a flight of stairs as the Enchanted Girl reminds her that Rapunzel will come for him, and that is when they will face off against each other, with Cassandra using the full power of the Moonstone against her former friend, while Varian wonders who Cassandra is talking to. Once they get to the throne room, Varian tries to talk Cassandra out of her quest for revenge against Rapunzel, as he has been where she is now, but she refuses to be swayed by his words, as she states that they are not the same, and she has nothing left to lose. With that, she imprisons Varian in a cage and sends him to hang helplessly while she prepares for her imminent battle with Rapunzel.
Meanwhile, Rapunzel and her friends have finally reached Cassandra's Dark Tower and are searching for a way in, but every attempt they make ends in failure, and Cassandra finds it amusing, until the Enchanted Girl orders her to let Rapunzel in so they can finish their fight. Reluctantly, Cassandra agrees and opens a path for Rapunzel to follow into the tower. Once inside, Rapunzel and the gang decide to split up to find out which path is the correct to take. She and Eugene take one path, while Lance, Kiera, Catalina, and Maximus take another path.
Back at the top of the Tower, Varian is revealed to have awakened in a Dream World, where he encounters the Enchanted Girl, who explains that, to save Cassandra, the final incantation must be used by the vessel of the Sundrop Flower, and against the power of the Moonstone Opal. Varian protests that there is no final incantation, but the Enchanted Girl states that he just needs to know how to look, saying he must use the sun to see the Sun. Upon falling off the ledge to avoid a fire, he awakens back in his cage in which Cassandra trapped him, and unrolls the Graphtic Scroll, pondering the meaning of "Use the sun to see the Sun".
Meanwhile, Rapunzel, Eugene, and Pascal make their way through the tower, with Rapunzel thinking that they could be walking into a trap. Pascal has an idea of being able to get in without being seen, while Lance and the others seem to be getting lost at every turn they take. He finds his way into Cassandra's throne room, just as she reveals herself, causing him to turn invisible. However, she finds the chameleon anyway and scoops him up off the floor.
As Rapunzel is waiting for Pascal's all-clear, she decides to follow him, before Eugene cautions her that there may be no way to reach Cassandra, and she may have to kill her. Rapunzel insists that she's not dealing with a monster and that Cassandra will come around, and heads upstairs to find Pascal.
Back in his cage, Varian becomes frustrated over the Enchanted Girl's riddle and tosses away the scroll and his goggles, which suddenly catch the sun's reflective glow and shine it at the scroll. On that, he realizes what the riddle meant, that the final incantation needs sunlight to completely read it, just as Rapunzel and Eugene enter Cassandra's throne room, where they find Varian in his cage. He reveals that he needs a concentrated beam of sunlight to see the final incantation clearly, but his goggles are too scratched up. Rapunzel has an idea of using the crystal in her engagement ring as a focusing lens, and has Eugene deliver it to him, just as the Tower starts rumbling and Cassandra reveals herself, having caged Pascal. She lets him go, and he runs back to Rapunzel's shoulder.
Cassandra informs Rapunzel that she made a mistake coming to her stronghold, and Rapunzel states that she will not leave until she resolves her differences with her former friend. In response, Cassandra closes up all the openings in the tower, trapping the twosome inside. Cassandra explains that the entire tower is made up of the Black Rocks, and she has complete control over them. As the Enchanted Girl orders Cassandra to show Rapunzel how powerful she has become, Rapunzel states that she will not fight Cassandra, and Cassandra remarks that killing her will be very easy. She tries to crush Rapunzel with a monumental Black Rock, but Rapunzel is able to protect herself by shielding herself with her hair. Then Cassandra crumbles that same rock under Rapunzel's feet, but the Princess is able to save herself from falling by using her hair to hang from the ledge, while Eugene is barely able to deliver Rapunzel's ring to Varian, who uses it to read the final incantation on the Graphtic Scroll. Unfortunately, the sunlight from the crystal on the ring is too focused, and it ends up destroying the scroll, but not before Varian is able to write the translation of the incantation on another piece of parchment.
Rapunzel manages to climb back into the tower, where Cassandra attacks with more Black Rocks and ultimately pins her opponent to the wall, despite the Princess' attempts to convince her to come back and her declaration that she will not fight her or justify her hatred. On this, Cassandra wills Varian's cage back into the tower, as she knows that Eugene is out there with him. She threatens to crush Eugene in a prison of Black Rocks if Rapunzel does not fight, but Varian reveals that he has the final incantation, and Rapunzel must be the one to use it, while Cassandra is wondering what he's talking about. As the Enchanted Girl orders Cassandra to finish the fight, Pascal snags Varian's new parchment with his tongue, and Rapunzel chants the final incantation, which causes her hair to glow and gives her the power to fight Cassandra on equal terms.
As Cassandra tries to impale Rapunzel with more Black Rocks, Rapunzel fights back by disintegrating them. No matter how many times Cassandra unleashes the Black Rocks against Rapunzel, it's useless now against the Sundrop's full power. As the twosome battle, a portal opens above the Enchanted Girl, and she disappears inside, just as both Varian and Cassandra are blasted out of the tower, with the Moonstone chipped at one spot. Varian is caught by Lance, who happened to be at the right spot to catch him, and is reunited with him, Maximus, Kiera, and Catalina, while Cassandra catches herself on a platform of Black Rocks. Rapunzel collapses from the expenditure of magic she used in the battle, but is able to get back onto her feet and share a hug with Eugene, who compliments her on such an amazing usage of her Sundrop powers.
Back at Corona Castle, Rapunzel and Eugene decide to postpone their engagement once again after such an incredible adventure. Lance, Kiera, Catalina, Maximus, and Shorty bring Eugene's birthday cake into the room, and Eugene proceeds to blow out the candles.
Meanwhile, back at the tower, Cassandra has climbed back into the remains of her throne room and gets the shock of her life when she sees that the Enchanted Girl has now gained a physical form. The Enchanted Girl remarks how the clash of Sun and Moon has released her from her prison and declares: "it's good to be back."
- Mandy Moore as Rapunzel
- Zachary Levi as Eugene Fitzherbert
- Eden Espinosa as Cassandra
- Jeremy Jordan as Varian
- James Monroe Iglehart as Lance Strongbow
- Jennifer Veal as Enchanted Girl/Zhan Tiri
- Vivian Vencer as Angry/Kiera
- Ruby Jay as Red/Catalina
- Julie Bowen as Queen Arianna
- Clancy Brown as King Frederic
- Bruce Campbell as King Edmund
- Paul F. Tompkins as Shorty
- Susanne Blakeslee as Old Lady Crowley
- Peter MacNicol as Nigel
- Rapunzel's engagement ring for Eugene strongly resembles his wedding ring in Tangled Ever After.
- King Edmund makes a reference to how he sent Eugene away as a baby in "Destinies Collide".
- Cassandra's entrance is a reference to Maleficent's entrance in Sleeping Beauty.
- Cassandra returns to Corona and reunites with Rapunzel for the first time since her betrayal in "Rapunzel's Return".
- Varian has moved his work to the Demanitus Chamber.
- The way Eugene and Lance try to climb up to the entrance of Cassandra's fortress, is a reference to The Emperor's New Groove where Kuzco and Pacha climbed up the cliff to get out and the palace to reach the potion.
- The scene where Rapunzel walked angrily to Cassandra is a reference to when Star Butterfly walked angrily to Toffee from the Star vs. the Forces of Evil Season One finale episode "Storm the Castle".
- Pascal pulling down on Maximus' ear is similar to how Sergeant Tibbs pulled down on Captain's ear in One Hundred and One Dalmatians.
- It is revealed that no one else besides Cassandra can see or hear the Enchanted Girl.
- Varian was only able to see and hear her when she entered his dreams.
- It also the second time Varian had a nightmare. The first was "Be Very Afraid".
- There are several sequences that reference scenes from "Secret of the Sun Drop", besides, Cassandra's actions are also similar to Varian.
- The main antagonist is Cassandra, someone who betrayed Rapunzel, like Varian.
- However, the Enchanted Girl is the true antagonist and is playing both sides.
- It's Eugene's twenty-sixth birthday, just like it was Rapunzel's nineteenth birthday.
- Varian is kidnapped by Cassandra, like he kidnapped Queen Arianna.
- Eugene tries to fight Cassandra with his sword, like how Cassandra tried to fight Varian with her sword.
- Cassandra traps Pascal in a cage, like how Varian trapped him in a cage.
- Cassandra fights Rapunzel, like Varian.
- Eugene and Varian are worried about each other after Rapunzel defeated Cassandra, like how Queen Arianna and King Frederic were worried about Rapunzel after she defeated Varian.
- Cassandra wants Varian to tell her the incantation, like how Varian wanted Rapunzel to help him free his father from the amber.
- Cassandra puts makeshift handcuffs on Varian, who tied Queen Arianna's hands via rope.
- Cassandra watches Rapunzel and her friends trying to enter the stronghold. Varian watched the Corona army going to his house.
- Rapunzel unleashed her Sundrop's full power with the black rocks to defeat Cassandra like she did to defeat Varian.
- The way Cassandra crashes Eugene's birthday party is like how an Automaton was in the castle.
- When Rapunzel passed out after Cassandra is defeated, she did so after Varian was too.
- Cassandra squeezes Eugene with the black rocks is similar to the way Varian squeezes Cassandra and Queen Arianna with the giant robot.
- Cassandra laughed evilly when she watched Rapunzel and her friends trying to enter the stronghold is similar to the way Varian laughed evilly when he welcomed back Rapunzel to his house.
- Varian was freed from the cage during the blast is similar to the way Queen Arianna freed herself with King Frederic's sword before she is encased inside the amber.
- Eugene running to Rapunzel after Cassandra is defeated is similar to the way Eugene ran to Rapunzel after Varian is defeated.
- Varian tries to reason with Cassandra after being captured by her but she ignored his pleas to stop becoming a villain, is similar to the way Queen Arianna tries to reason with Varian after she was captured by him but he ignored her pleas to stop becoming a villain.
- Rapunzel is quoting the song The Girl Who has Everything at the end of this episode is similar to Varian quoted the song Let Me Make You Proud.
- Old Lady Crowley briefly sings The Girl Who Has Everything in this episode is similar to the way Shorty briefly sang the Wind in My Hair.
- Varian trying to reason with Cassandra by singing Nothing Left to Lose in this episode is similar to Rapunzel trying to reason with Cassandra by singing Crossing the Line in "Rapunzel's Return".
- Even though Cassandra claimed that she and Varian are not the same as he tries to reason with her during Nothing Left to Lose, a few of Cassandra's actions towards Rapunzel, Corona, and the people that the princess cares about were somewhat similar to the ones that Varian had done toward them in "Secret of the Sun Drop".
- Eugene, Lance and Maximus being chased by a large boulder is a reference to Indiana Jones and the Raiders of the Lost Ark.
- The Enchanted Girl gains a physical form.
- Prior to that, the silhouetted appearance she briefly takes on during the battle between Rapunzel and Cassandra resembles Zhan Tiri, heavily implying she is indeed her. This is confirmed in the next episode.
- The end credits do not play the usual song in this episode.
- The stuffed monkey with cymbals Eugene is carrying resembles the Monkey from Toy Story 3.
- Near the end of the episode, both Cassandra and Varian fall off Cassandra's Stronghold. However, Varian falls into the arms of Lance, whereas Cassandra has to save herself using her powers. This reflects how Varian's redemption has led him to be surrounded by friends once more while Cassandra's path of hatred and darkness has left her with no one but herself. (even though we can see by the way Kiera and Catalina facepalm that Lance catching Varian was a complete accident/coincidence)
- Zhan Tiri makes a reference to this episode that Cassandra lost before she began because of her ego, the same as her mother did, in the series finale, "Plus Est En Vous".
- Rapunzel says, "Cass is sending a message. She wants me to know that everything that once was mine, will belong to her". This is a reference to the lyric "Bring back what once was mine. What once was mine" from Healing Incantation.
- This episode appears to skip Rapunzel's 21st birthday as it mentions Frederic and Arianna's anniversary taking place six months prior to the episode. As both events take place on the same year, then this episode appears to take place 3 months after Rapunzel's 21st birthday.
- Cartoon Physics: The top floor of Cassandra’s tower is above most of the clouds, enough to induce hypoxia. It is also mostly open to the lack of air. However, in this episode and all subsequent episodes, characters never suffer from hypoxia.
- In the German dub, Varian briefly spoke with his singing voice after his half of Nothing Left to Lose.