"Reign Storm" is the first Danny Phantom movie, comprising episodes twenty-four and twenty-five. When Vlad Plasmius accidentally awakens Pariah Dark from his eternal slumber, the king of ghosts reigns terror on Amity Park. Now Danny Phantom and his enemies must band together to stop this super ghost from taking over Earth and the entire Ghost Zone.
Vlad Masters is in the Ghost Zone, at Pariah's Keep, looking for the Ring of Rage and the Crown of Fire, ancient artifacts that belonged to Pariah Dark, one of the most powerful ghosts in Ghost Zone history. Vlad manages to find the Ring of Rage easily, but when he goes for the Crown of Fire, he opens Pariah Dark's Sarcophagus of Forever Sleep, reawakening the ghost king. Vlad attempts to run away, but is shot with an ectoplasmic beam straight through the Fentons' Ghost Portal. In the Fenton Works lab, Jack and Maddie work on the Fenton Ecto-Skeleton, a battle suit designed to beat back even the most powerful of ghosts. Vlad crash lands nearby and struggles for Jack's help. Meanwhile, a duplicate of Vlad makes a deal with the Fright Knight.
Danny heads for school, happy he stopped ghosts and finished his homework in time. His happiness ends when Dash and Kwan chuck a football at him. Danny retaliates back by shooting a small ghost ray to knock a sign down in their path and later stuffing Dash's locker with toilet paper. Dash, angry, chases Danny into the cafeteria. He hides under the a table inhabited by geeks. He also finds Valerie under the same table, hiding from Nathan because he keeps asking Valerie to the senior prom, despite it being three years away. Danny and Valerie start a friendly conversation, finding out they have more in common than they realize.
After school, the two continue running from their current problems. They come across Sam, hiding from her mother (who wants her to try on a perky dress). Sam isn't too pleased to see them hanging out together, worried for Danny's sake as the three run to hide in the Fenton household. Inside however, Danny gets a surprise when he sees Vlad in the living room with his parents and Jazz. Vlad reveals his plan aloud to steal the Ecto-Skeleton that Jack and Maddie have been working on, merely claiming he's "joking". Afterwards, he turns his attention to Valerie who (as well as Danny) is shocked Vlad knows her.
An alert goes off with Maddie claiming that a huge ghost attack is on its way. While Danny goes into the Ghost Portal to stop the ghosts, Sam and Jazz trip the parents to buy Danny some time. Vlad, meanwhile, converses with Valerie. Danny heads to the basement lab. To his relief, Box Ghost pops out. Then more ghosts (most of whom he has fought previously) come out of the Fenton Portal, escaping the Ghost Zone. Danny and Skulker fight and they end up outside, though Sidney Poindexter expresses that Pariah Dark is a more important threat. That doesn't stop the ghosts from attacking Danny, causing him to nearly fall unconscious and transform back into his human half.
Meanwhile, Vlad tells Valerie that he supplies her with ghost hunting gear because he's impressed by her abilities and determination, and gives her the Ring of Rage for reasons he does not yet say. Meanwhile in the Ghost Zone, Pariah Dark readies his army.
The next day at school, Dash messes with Danny some more, causing him to further abuse his ghost powers on Dash, something Sam isn't too keen on. Back at the Fenton lab, the Fright Knight takes Maddie captive. Jack uses his incomplete Ecto-Skeleton to quickly beat up the Fright Knight and rescue Maddie, though the Ecto-Skeleton drains him of his energy and nearly kills him.
Pariah's ghost army attacks Amity Park, causing a widespread panic. In the meantime, all the ghosts take this time to claim a new haven, invading various stores in the human world to hide in (except Sidney, who feels they're merely bullying their way in). Tucker, Sam, Danny's parents, and Valerie's father Damon Gray watch reports about the ghost invasion on TV.
Tucker and Sam express their concern about Danny spending time with Valerie. Danny, however, enjoys her company, and Valerie (who comes from behind) thinks the same of him, too. Danny's ghost sense then goes off so he runs, only to bump into Dash. Using his ghost powers again, Danny overshadows Dash and smashes him to the lockers repeatedly. He resumes running off and finds Vlad. Vlad points out how Danny used his powers to get revenge on bullies and that Danny and Vlad are not so different, both using their powers for personal gain. They then fight. While Danny fights off Vlad, Valerie makes note of Sam's crush on Danny, warning her she better make a move before someone else does.
Vlad leads Danny to the football field where Vlad tells him he has a much bigger threat to fight off, as Fright Knight and his army are there. Vlad helps Danny fight off Fright Knight and his army. As they fight, Valerie comes along and attacks the two, but Danny manages to persuade her to trust him and fight alongside him.
The Fright Knight puts his sword in the ground and states a royal decree of the Ghost King, which creates a massive Ghost Shield around the entire city. He states that the barrier will only be removed if the humans give up the Ring of Rage, and any human removing the sword generating the barrier is an act of surrender. Valerie continues to fight the Fright Knight, only for her to be knocked unconscious.
Afterwards, Maddie arrives in the Fenton RV with Damon and the other parents to collect their kids. At the Fenton household, Vlad helps Maddie build the rest of the Ecto-Skeleton while Sam and Tucker discuss with Danny further on his close contact with Valerie, thinking the ring on her finger is used for ghost detection. They suppose the ring is the one Fright Knight mentioned, and leave to gather more info.
They find Skulker and Danny and him fight. Sidney quickly breaks it up by telling Skulker that Danny could help them. Skulker takes Danny, Sam, and Tucker into the hideout where all of Danny's enemies in the Ghost Zone are staying. Skulker then tells them all about Pariah Dark: a powerful ghost who ruled the Ghost Zone with an iron fist, drawing unlimited power from the Ring of Rage and the Crown of Fire, until a desperate move got him to be sealed for all eternity... or so it seemed, until Vlad reawakened Pariah Dark. Danny afterwards tries to get all the ghosts to ally with him and fight Pariah, but they all merely laugh and leave, causing Danny to go at it alone.
Later near his house, Danny requests for Vlad and confronts him asking for the ring back, leading the two to fight each other again (going back to the football field from earlier) while Vlad continues to manipulate Danny, stating he is more like him then he knows. Vlad's mocking frustrates Danny, causing him to pull Fright Knight's sword. This activates Pariah's decree, pulling the entire town into the Ghost Zone. The invading ghosts resume their march, and Fright Knight and Pariah arrive. Pariah easily defeats Vlad and Danny. Jack and Maddie announce to the town to hide under the Fenton Ghost Shield, which Damon increases the size of as well as sends out a Ghost Probe.
Pariah Dark would have destroyed Danny and Vlad if not for Valerie, who comes and rescues the two while sending the ring flying away on a missile. Pariah heads for the ring while Fright Knight gives chase until she manages to get over to the other side of the Fenton Ghost Shield. She then takes the two to Danny's room, where she rests herself from her own injuries. Pariah captures the missile and puts on the ring, regaining his full powers.
Vlad leaves, using his intangibility, by the time Jack and Maddie come to check up on Danny and Valerie, assuming they're just hanging out. After leaving, Danny wakes up and is reunited with Tucker and Sam, where he shares his guilt for not fixing this problem sooner. Seeing it as his responsibility, he heads to the basement with Sam and Tucker, watching from above as his parents and the other adults discuss the Ecto-Skeleton. Every parent, as well as Jazz, argue over who gets the suit, knocking each other senseless. Danny then heads over to get the suit, only for Valerie to block his path. When Damon comes downstairs, Danny takes advantage of this and removes her mask, thus buying him enough time to go intangible and grab the Ecto-Skeleton while Damon berates his daughter for her current dangerous job as a ghost hunter.
Danny prepares for battle atop the Fenton roof, while Tucker and Sam watch emotionally, afraid for him due to the suit's unreliability. Danny tries to reassure them, but asks if they have anything to say. Sam tries to express her feelings, but Pariah appears, giving a message to the humans. Danny then goes off to fight as he goes ghost, giving the Ecto-Skeleton a touch of his own personality as well. He then gets Tucker to prepare to lower and raise the ghost shield as he leaves. Everyone cheers on "Inviso-Bill", to which Danny corrects as "Danny Phantom" before heading off to fight Pariah.
Pariah's castle is guarded by a seemingly infinite number of ghosts, and Danny uses a lot of energy trying to destroy them, though when it appeared he had no chance, Sam and Tucker arrive in the Specter Speeder, where they drop off many of Danny's ghost enemies, all who help Danny fight off the army and get him into the castle. Once inside, Danny finds Pariah, where he begins to battle him as the suit slowly drains away his life force. While Pariah puts up a good fight, Danny duplicates himself for the first time (thanks to the suit extending his power), to easily outmatch him and remove his crown. As Danny stuffs Pariah in the coffin, the suit nearly drained away his life as he does so. Vlad locks Pariah in place and Amity Park returns to its original home. Afterwards, Danny passes out.
When Danny wakes up, he finds himself surrounded by his family, Sam, Tucker, Valerie, Damon, and Vlad. Maddie expresses how Vlad rescued him, no longer hating him for doing such a kind thing. Later on, the news states the current recovering of Amity Park as well as Inviso-Bill, now understood to be Danny Phantom, to be a hero to the majority of Amity Park (with the majority of his supporters up to 64%). The next day at school, feeling guilty for abusing his powers, Danny goes to apologize to Dash, who then hangs him to the flag pole by his underwear as Dash's own way of accepting said apology. Meanwhile, Valerie goes to Tucker and Sam, stating she is starting to like Danny, something neither Sam and Tucker enjoys. As a result, they send Nathan after her.
- All of Danny's main villains return, except Youngblood, Kitty, and Freakshow (Youngblood was trapped underwater in "Pirate Radio").
- Danny's battle with King Pariah is later referenced in the episode "Infinite Realms" as the reason for Frostbite and his people's great respect towards Danny and the title "The Great One" they give him.
- Allusions: See List of allusions
- Goofs: See List of goofs
- The ghosts' hiding places:
- "Reign Storm" is the only Danny Phantom television movie in which Danny does not reveal his secret to his parents (and the rest of the world). Instead Danny reveals Valerie's secret to her father.
- Though most of Danny's enemies appear, Kitty, Bertrand, and Youngblood are noticeably absent. Though Youngblood was likely still trapped in the ghost shield underwater from the previous episode.
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