Goh is scanning the news on his Rotom Phone and learns the Legendary Pokémon Ho-Oh was recently sighted. He rushes over to Professor Cerise, who informs Goh and Ash that Ho-Oh is deeply connected to Johto folklore. Ren and Chrysa reveal that all Ho-Oh sightings have occurred around Ecruteak City. With that, Ash declares that he will battle Ho-Oh, though Goh is determined to actually catch it.
The boys arrive in Ecruteak City via bus. Relying on Goh's research, they head directly for the Bell Tower, and on the way there, Goh catches a Sentret. Ash reminds Goh that they should be focusing on Ho-Oh as their main target, and to their surprise, one is flying overhead. Ash has Pikachu use Thunderbolt on the Legendary, and shockingly the attack lands and does serious damage. The Ho-Oh begins to land, and the boys trace it directly to the Bell Tower grounds, where it is revealed to be a Fearow and Cyndaquil in disguise. Their Trainer, a boy named Chad is furious despite Ash's apology. Goh asks if Chad was behind the recent Ho-Oh sightings, and Chad instantly turns away to hide the hoax. His grandfather, Jaye, with a Hoothoot on his shoulder, is also disappointed in Chad's actions. Jaye reminds his grandson that Ho-Oh doesn't exist, but Ash refutes the claim and recounts that he first saw Ho-Oh on the day he set out to become a Pokémon Master. Jaye says Ash simply thought he did before walking off.
The boys seek shelter under the stoop as it begins to rain down. Chad informs Ash and Goh that his grandfather used to believe differently. He had shown Chad a Rainbow Wing from his encounter with Ho-Oh, even traveling around to find the Legendary again. Though Jaye grew disheartened one day, and began to believe finding Ho-Oh was a thankless task. Chad explains that he has his Pokémon disguised as Ho-Oh in an attempt to cheer up his grandfather. Ash suggests they find the real one instead of lying. Chad admits that his grandfather tried for decades. However, Goh is more optimistic, and explains an ancient legend that says Ho-Oh will arrive when a Rainbow Wing is waved at the top of the Bell Tower. Chad replies that his grandpa tried this approach several times already, but it didn't work.
Goh suggests they explore the Bell Tower anyway, so the group of boys step inside. They spot a golden mural depicting Ho-Oh flying with a rainbow behind it. Goh suggests that Ho-Oh must have some connection to rainbows, and Ash affirms this when thinking back to his own encounter. Goh turns to his Rotom Phone to check the weather conditions over Ecruteak, and reveals that the moving clouds and low sun exposure are the perfect rainbow-creating conditions. The boys settle on a plan - they will wait for a rainbow to appear before waving the Rainbow Feather at the top of the Bell Tower. Chad suddenly rushes out, and later returns with the Rainbow Wing and his doubtful grandfather.
Together, the eight begin the ascent up the many stairs to the top of the Bell Tower. A wild Misdreavus begins playing tricks with its disorientating illusion, using Confuse Ray to make the stairs seem very soft and wobbly. They find it difficult to even stand upright, and Ash's right foot begins to sink in the stairs, as if in quicksand. Misdreavus transforms the stairs into a steep ramp, sending everyone back to the first floor. A Stantler appears and induces another illusion using the waves emitted from its antlers. They suddenly find themselves hanging on the edge of a very steep cliff. After much difficulty, they finally conquer the steep cliff climb, only to find themselves now surrounded by a desert. Goh turns to his Phone for answers, but the screen is only showing static, and saying that it's unable to pinpoint their location. Jaye realizes they must be caught up in an illusion, and has Hoothoot use Foresight to transport them back to reality. Goh immediately spots the culprits, Misdreavus and Stantler on the next floor. Stantler prepares to put everyone under an illusion again, though Goh catches the two Pokémon before that. Chad is impressed by Goh's easy catches, and Goh replies that he aims to catch every Pokémon.
Ash and the others eventually reach the outdoors. They pause momentarily after coming across a fleet of worn stairs, helping each other up to the top floor. Goh is relieved to see the rain has now stopped. Chad proceeds to wave around the Rainbow Wing and calls out to Ho-Oh. Moments pass, when suddenly a rainbow appears in the sky. Chad again calls for Ho-Oh. A rush of wind blows the Feather out from his hand, though Jaye catches it. Jaye admits he has learned a lot from today and goes on to wave around the Rainbow Wing in a bid to finally meet Ho-Oh. Ash, Goh, and Chad are all greatly encouraged by Jaye's regained hope, and chip in to call for Ho-Oh. However, they soon stop, as their calls go unanswered. Jaye isn't disappointed, and instead asks Chad to accompany him during his future searches. Chad happily agrees to it. Unexpectedly, the Wing begins to glow in all colors of the rainbow. Ash's stomach grumbles, so Chad invites him over to his house for some homemade curry. As the three boys begin walking away, Jaye catches sight of Ho-Oh in the distance. He calls for the boys to turn around, but it is too late. Nonetheless, Jaye smiles having finally caught sight of Ho-Oh after many decades.
Ash and Goh later return to the Cerise Laboratory, reporting back of the fake sightings. Goh remains focused on his primary goal to catch every Pokémon including Mew, while Ash vows to become a Pokémon Master.