After getting himself a coffee, Ren starts to walk back to the lab. He stops after hearing an odd sound, but quickly dismisses it as the wind outside. A few more steps and he suddenly pauses as a dark shadow casts itself over him. Ren turns and screams as he sees the ominous Gengar that has been haunting the Cerise Laboratory. Ash and Goh rush out of their room to find Ren slumped against a wall. With tears in his eyes and still shaken, Ren explains that Gengar is back. The boys are thrilled by the news and leave to go catch Gengar for themselves.
Another scream, this time from Chrysa, leads the boys downstairs. Chrysa and Mimey explain that Gengar just appeared, hence the mess. Suddenly Pikachu is thrown into the air, though Ash catches him in time. Gengar then starts throwing various items at Ash, but becomes frustrated at the lack of a reaction and simply materializes in front of everyone. Gengar launches a barrage of Shadow Balls, frightening everyone. It fades away after Ash orders it to stop, leaving Goh perplexed that Gengar listened at all. Professor Cerise, Ren and Yamper enter the room and start to clean up following Gengar's antics. However Gengar hasn't completely disappeared, rather it has now attached itself to Ash's shadow.
Chrysa and Ren wonder why Gengar is haunting the lab, and the Professor sits everyone down to explain. Prior to purchasing what is now the Cerise institute, the building was rumored to be haunted by a poltergeist. Professor Cerise explains that he has experienced doors slamming, sudden blackouts and things moving, but he was fine as it always settled down quickly. Chrysa and Ren are not surprised by the Professor's admissions. Goh says Gengar must have stopped trying after realizing Professor Cerise was unfazed by its antics, but cannot figure out why the haunting has started up again. Chrysa suggests that Gengar must be upset with all the new arrivals, including themselves, Ash, Goh and the Pokémon. Ash suddenly feels a chill down his arm, and Goh suggests that he must have been cursed by Gengar. Professor Cerise says that Gengar cursing someone is just a hypothesis, which Ash agrees by dismissing the claim, even after a series of unfortunate events like his chair breaking and being trampled by the Pokémon.
After the ground collapses under his feet, Ash and Pikachu rush out of the Cerise Laboratory to clear their heads. Gengar, who has attached itself to Ash’s shadow, is inadvertently dragged along and begins to panic from leaving the Institute. After a while, both Ash and Pikachu are feeling better from the run. They continue through the streets of Vermilion City, even passing Team Rocket who are sitting down at a local café. As Ash rounds another corner, he bumps into a guy, knocking them both over. Gengar sneers for a moment until he recognizes the other person. Ash apologizes, while the guys suggests he watch where he is going next time. The man’s girlfriend suggests he must still be cursed, but the guy admits that was three years ago. Goh catches up just as the man says that he is glad “it” is now gone as he was never able to win any battles or catch any Pokémon. Gengar is angry to hear this, and recalls that it was abandoned by the man three years ago. Its Trainer promised to return, though Gengar was left at the abandoned site that later became the Cerise Laboratory. Gengar became angry as time passed and it was still waiting for its Trainer to return. It deliberately scared off potential buyers of the building with its antics.
As Gengar's former Trainer declares that he should never have caught the miserable Gengar, the Ghost Pokémon makes its presence known. Gengar launches a Shadow Ball at its former Trainer, narrowly missing him. Ash orders the raging Pokémon to calm down, and has Pikachu use Electroweb to stop a barrage of Shadow Balls. Ash turns his attention to the man. Gengar prepares to lash its former Trainer with a large Shadow Ball. The man repeats his irritation with Gengar and blames it for cursing him before rushing off with his girlfriend. Gengar doesn’t end up launching the attack and disappears when Ash tries to talk to it. Ash is furious that Gengar was mistreated in the past, so he and Pikachu run off to find it. Goh stays behind, remarking this is just like Ash. Scorbunny notices the Poké Ball in Goh's hand, but Goh assures his partner that he simply wanted to catch Gengar for himself and not help Ash. Scorbunny knows it is right, and Goh admits they should help look for Gengar as well. Watching from a distance, the Team Rocket trio are also interested in recruited Gengar to their team.
Team Rocket are first to find Gengar, who is sitting by itself. They invite Gengar to join them, explaining the "benefits" like pursuing a path of evil and being able to crush enemies with limitless power. Gengar turns away and, as translated by Meowth, it says that it cannot trust humans. Team Rocket change tact, and James traps Gengar inside a vacuum tube. Gengar becomes increasingly furious, however Jessie dismisses its feelings. As the trio prepare to walk off with their catch, Pikachu breaks the capsule and frees Gengar with an Iron Tail. Jessie is particularly irate to see Ash and Pikachu again interfering with their plans. Ash suggests Gengar help him defeat Team Rocket, taking the Shadow Pokémon by surprise. Ash elaborates that it should forget about its old Trainer. He explains that it doesn’t have to trust him right away, but Ash admits he already trusts Gengar. With that, Gengar sneers and steps forward to take on Team Rocket with Pikachu.
Team Rocket call on their own support. Pelipper flies by and delivers the Rocket Prize Master. With a turn of the machine, Jessie and James receive a pair of Dusclops. Their Rotom Phone provides the trio with some additional information on Dusclops. Ash is excited that it will be a Ghost-type clash. Jessie calls for a Shadow Sneak attack, though Pikachu rushes into a Quick Attack to dodge. James orders an Ice Punch, freezing Pikachu's foot in ice. Gengar fires off a Shadow Ball at its ally, freeing Pikachu off the ice, and Ash thanks it. Gengar twirls around to dodge an approaching Fire Punch before blocking James's Dusclops using Night Shade with its own attack. The other Dusclops strikes Pikachu with a Fire Punch. Jessie then calls for Night Shade as well, though Gengar manages to hold the two Night Shade attacks with its Night Shade and eventually overpowers the Dusclops. Gengar suddenly vanishes before reappearing to deliver an Ice Punch on its opponent. Ash calls for a finishing Shadow Ball, which blasts Team Rocket off. Goh is impressed by Ash and Gengar's joint efforts. Ash remarks that Gengar actually did the work, and thanks the Ghost type. Ash suggests they should return to the Institute. Gengar walks over to Ash, who unexpectedly faints only for Gengar to catch him in time.
Later, Ash wakes up to find himself in his dorm room. Goh explains that Ash had a fever, and apologizes for blaming Gengar on placing a curse on him. Ash is instantly reminded of Gengar, and asks where it is. Ash is then hit by an apple followed by a Poké Ball. Ash realizes Gengar must want to join him, so he calls out to the Ghost who instantly materializes in the room. Ash asks if it wants to join him, and Gengar gives a faint nod of approval. With that, Ash tosses the Ball and the Ghost type is officially caught. Ash is thrilled and calls out Gengar to welcome it onto his team. Gengar however disappears again and makes apples rain down on Ash. Goh suggests Ash should eat up if he wants to get better anytime soon, and Ash obliges, finding the apples to be delicious. Meanwhile, Gengar is standing on the Institute’s tall spire and happily enjoying an apple.