Plotline
The story opens up ten years in the future in a derelict Amity Park. A rogue ghost tears down the city's powerful ghost shield with a mysterious power called the Ghostly Wail. An adult Valerie appears to stop the ghost, and the ghost is revealed to be Dark Danny: Danny Phantom's evil older self.
Somewhere in the Ghost Zone, two ghosts called the Observers have taken notice of the destruction of Amity Park. A ghost named Clockwork states that "Danny will become a threat to us all." Clockwork then decides that he will make sure that Danny never becomes evil.
Back in present day Casper High, Danny is worrying about the upcoming Career Aptitude Test (C.A.T.) that determines a person’s future, since he has not had much time to study. Mr. Lancer announce if the person fail the test he/she will be doom to a career at the Nasty Burger. Sam then appears and tells Danny that ghosts are inside the school. Tucker comments that Danny will grow up to be a ghost hunter and Danny replies that "a ghost hunter isn't a real career path."
After defeating the ghosts in the school, Danny returns home to FentonWorks where Jazz suggests that Danny get to work studying. Danny retorts saying, "You're brilliant and I'm stupid and I'll never be able to get as high a score on my C.A.T. as you did." A ghost suddenly appears behind Danny and he yells for Jazz to get out of his room, despite being in the kitchen. Jazz gets the hint and leaves so Danny can fight the ghost.
The ghost then reveals herself to be Box Lunch, the daughter of the Box Ghost and the Lunch Lady. Danny finds this realization very disturbing ("Eww. That's just gross!"). Danny then transforms into Danny Phantom and defeats her but destroys the Nasty Burger in the process by causing the Nasty Sauce to explode. Danny finds a curious medallion Box Lunch left behind when she disappeared. Danny also accidentally phased through Mr. Lancer's briefcase where Lancer was keeping the C.A.T. answer booklet and after finding the booklet stuck to his back, realizes this is the answer to all of his studying problems.
Meanwhile, the Observers comment on this development revealing that they planted the test answers for Danny to find. The Observers are convinced Danny will become evil, but Clockwork insists otherwise. The Observers also notice the fact that Danny has discovered Box Lunch's time immunity medallion.
Back in Danny's room, Tucker examines the medallion. Sam decides that the medallion seems futuristic and then asks Danny what he plans to do with the exam answers he found. Before Danny can debate about it, a ghost named SkulkTech 9.9 (the future Skulker and Technus combined) appears. Danny tells Sam and Tucker to find out what they can about the medallion while he goes to fight the ghost.
After SkulkTech 9.9 introduces himself, Tucker comments he can hack into the ghost to stop him. SkulkTech 9.9 leads the battle back to the Nasty Burger and comments that although "The Pummeler" does not work on Danny in the future, it will surely work in the present time. Danny is confused by this but he battles and defeats the ghost.
Using SkulkTech 9.9's time immunity medallion, Danny, Sam, and Tucker arrive in Clockwork's lair where Clockwork reveals himself as the master of time and battles Danny. The trio then determines Danny's turning point was cheating on the C.A.T. Clockwork explains that in the future, Danny has completely lost his humanity. Clockwork states he tried to change Danny's past, but since that did not work out, he'll simply have to kill Danny. Danny, Sam, and Tucker then escape to the future.
The trio is surprised to see Amity Park in a state of ruin and then come across the future Valerie. Not realizing Danny is from the past, Valerie mistakes him for being Dark Danny in disguise and attacks him until Sam and Tucker stop her. Valerie is shocked by seeing them and reveals that in the future they are both dead and claims it was all Danny's fault. The real Dark Danny then appears and claims responsibility for Sam and Tucker's deaths. Valerie tries to stop him but is defeated. Danny manages to save her. Valerie says that she forgot how cute younger Danny was. And then she passes out. Danny urges Sam and Tucker to take off the time immunity medallions and return to the present before Dark Danny can harm them. Danny is about to do the same when Dark Danny fuses the time immunity medallion inside Danny's body, trapping him in the future. Danny and Dark Danny fight, but Dark Danny then throws Danny into the Ghost Zone in hopes that Danny will never escape. And Dark Danny travels to the past to ensure his past remain unchanged.
In the Ghost Zone, Danny realizes his only hope to get back to the present is to find Vlad Masters and pray that he can fix this mess. After finding Vlad's ghost portal however, Danny accidentally stumbles across Walker and his police force and fights them.
In the television series, in the Ghost Zone Danny encounter older-versions of Box Ghost, Ember, Johnny 13, and Kitty. When Danny thought he was finish he unleashes his Ghostly Wail and defeats them all at once. Then the Boo-oommerang hits his head with a note sent from Jazz 10 years before to inform him that Vlad Masters should have the solution to the situation.
Danny finds an older Vlad on the other side of the portal and Vlad explains what happened ten years ago and how Dark Danny was created using the Ghost Gauntlets.
After Danny’s friends and family (including Mr. Lancer) were killed in an explosion at the Nasty Burger by his alter ego because he was caught cheating on the C.A.T., he had to live with Vlad. Surprisingly, instead of trying to hurt Danny he sympathized with his pain. After much mental suffering, he wanted the ghost side of him ripped out of his body. It was successfully done, but the ghost was evil and ripped out Vlad's ghost as well. Then the two merged, and seeing as they didn't need Danny's body anymore, that blew up Vlad's mansion, killing Danny and destroying everything. Dark Danny was born.
Danny then asks for Vlad to use the Ghost Gauntlets to remove the time immunity medallion from his body so he can defeat Dark Danny and set everything right again. Vlad argues that doing such a thing might kill Danny, but Danny comments that he's sure that Vlad can do it. After Vlad successfully removes the medallion Danny returns to the present and rushes to the Nasty Burger to have one final confrontation with his older self. Danny uses the Ghostly Wail, much to Dark Danny's surprise, and traps Dark Danny in the Fenton Thermos. Danny is about to go save his family when he realizes he cannot transform into Danny Phantom due to exhaustion. Clockwork appears however and sets everything right again.
At school, Danny turns the C.A.T. answer booklet in to Mr. Lancer and he decides to allow Danny to take the make-up exam the following week, preventing the tragic future.
In the television series, Jazz reveals her awareness of Danny’s ghost side. Clockwork takes the responsibility of watching over Danny so the future will be kept safe.
Read more about this topic: Danny Phantom: The Ultimate Enemy