
Danny Fenton is losing his mind! At least, that's what Jazz decides when her little brother starts acting strangely and fighting ghosts that aren't there. In reality, Danny is being tormented by a revenge-seeking Youngblood, who cannot be seen by adults -- or by big sisters who think they're adults. When Jazz sells the family on a ghost-tech-free camping trip, Youngblood follows and unleashes a series of juvenile attacks that make Danny seem even crazier, and put the Fenton family in danger.
Danny and Sam get into a fight, and when Sam utters the words, "I sometimes wish I'd never met you," she finds herself in a world in which she and Danny are strangers. Worse than that, since it was Sam who encouraged Danny to check out the Fenton Portal the night he got his ghost powers, Danny doesn't have any powers! Now, Sam must convince Danny that they share a friendship and a history, and lead him back to the Fenton Portal for a second "accident" so he can again become Danny Phantom.
After being bitten by tiny green ghost beetles, the kids of Casper High get a mysterious illness that gives them ghost powers and are quarantined at a spooky old hospital outside of town. When Danny sneaks into the hospital to investigate, he is captured by Penelope Spectra and her assistant, Bertrand. They are the ones who started this illness as part of their plan to build Penelope a young and beautiful new body. All she needs is Danny's half-human/half-ghost DNA to complete her ghostly plan. With Danny captured and Sam sick, it's up to Tucker to conquer his fear of hospitals and free Danny before Penelope gets what she's after.