Ash and friends are still on their way to Fallarbor Town and stop by Lake May for a rest, where they spot an Illumise and some Volbeat practicing for the May Festival. The Volbeat Trainer, Romeo, is a big klutz, and he causes an accident that sends all of the Pokémon crashing into the water. Ash and Brock send out their Water-type Pokémon to save them.
It turns out that Romeo is in love with the Illumise Trainer, Juliet, and he gets nervous around her. May decides to help him practice confessing how he feels by having Ash dress up as Juliet.
Meanwhile, Team Rocket has Meowth pose as a Volbeat, luring Illumise into a trap. Juliet goes searching for her Pokémon and instead comes across Romeo rehearsing with the kids. Romeo sends all of his Volbeat to track down Juliet's Illumise.
Team Rocket uses Sweet Scent to lure all of the Pokémon into a powerful vacuum, capturing Ash and Pikachu in the process. Pikachu shocks the vacuum to shut it down, and the one free Volbeat uses Quick Attack to destroy it, freeing everyone. The combined Volbeat use Signal Beam to send Team Rocket blasting off again.
Romeo confesses how he feels to Juliet, and they decide to marry. At the May Festival, the Volbeat and Illumise put on a spectacular performance.
Still on their way to Fallarbor Town, Ash and his friends find themselves along the shore of Lake May, a coincidence that doesn't fall short on Brock or May, as she comments on the comparison of the lake's beauty and herself. Max disagrees; May isn't thrilled. Ash then points out something is hovering over the lake's surface. It is an Illumise with a yellow bow around her neck, who displays her grace by gently touching the water in a pose, rippling the surface. Ash comments they haven't encountered one of them yet, and May subsequently points out another one they haven't seen before. It's a Volbeat with a red bow, flying across the lake. Volbeat flies up to Illumise and the pair begin dancing in the air. Brock identifies them as Volbeat and Illumise, prompting May and Ash to pull out their Pokédexes. While watching, a Nurse Joy greets the group, asking of they are here for the May Festival, for the dance performance of Illumise and Volbeat. She notes that it is almost time for the practice runs, and indicated two people standing out on the lake's pier, saying they are Volbeat and Illumise's Trainers, Romeo and Juliet. Brock is immediately smitten for Juliet, though May and Max manages to pull him away.
Juliet introduces herself to the audience gathered at the lakefront, promising to make it a success; Romeo stands behind her, silent and somewhat dejected-looking. Nurse Joy goes on to comment to the group about a local legend, that anyone in love who watches Illumise and Volbeat dance together will be blessed with good luck. On the pier, Juliet tells Illumise it's time to start practicing and twirls a conductor's baton with a light at the tip of it, ordering Illumise to use Sweet Scent. As Illumise does, Juliet turns to Romeo and asks him to release more Volbeat. He complies, but the belt pack he carried them in falls onto the pier, with four Poké Balls rolling out. Juliet concernedly comments on this, indicating it is not the first time this has happened. Remorsefully, Romeo begins to gather them up. Brock isn't impressed with Romeo at all, though Ash shouts out encouragements. Romeo thanks him before calling out the rest of his Volbeat, and tells his lead Volbeat it's time to start. Volbeat leads the now-quintet across the lake, but he's distracted by his feelings of love for Illumise and simply starts chasing her around, the rest following. Juliet is dismayed and orders Romeo to conduct his Volbeat properly. Frozen, Romeo attempts to regain his composure and his Volbeat with a baton, but he drops it onto the pier. At Romeo's cry, Volbeat stops to help, but ends up colliding with Illumise by accident, sending all five Volbeat and Illumise into the lake. With Illumise not resurfacing, Juliet dives into the lake, accidentally knocking Romeo into the water. As the chain of disastrous events unfold Ash and Brock dive into the lake with their Water Pokémon. The rescue team brings Romeo, Juliet, the Volbeat and Illumise onto the pier to recover from their near drownings. As Brock brings Juliet a towel, which she thanks him for, but is more concerned for Illumise, who is in Nurse Joy's care. Illumise appears to be fine, though Nurse Joy tells Juliet it would be a good idea to give Illumise a check-up, and recommends Romeo do the same. Romeo thanks Ash, and introductions are finally made. Romeo is impressed with Ash's passion, comparing it to his lack thereof, and accidentally sits on the spikes of Corphish's head. Meanwhile, Team Rocket are watching them, and Jessie hopes Romeo is alright, so she can see the Volbeat and Illumise dance and be brought good luck. James says it's only for people in love, but Jessie rebuts him, claiming she's already in love with a prince charming figure from her own fantasies. Meowth suggests catching the Firefly Pokémon for the Boss, because they could be dancing entertainment. Predictably, the other two are enthused.
At the Pokémon Center, Nurse Joy returns Romeo's Volbeat. As thankful as he is, Romeo remains distressed, fearing he'll simply mess up the act again. The others offer to help him practice, and Romeo cheers up somewhat. Outside on the lakefront, however, it becomes obvious Romeo isn't as clumsy as he first appeared to be, directing the Volbeat with little issue. He says he's fine when he practices alone, but he and his lead Volbeat, nicknamed Beat, tend to mess up when practicing with Juliet. May, however, senses what the problem ultimately is, and asked Romeo how he feels about Juliet. Claiming his chest tightens, his heart races, his hands sweat, and generally acts goofy when near her, May accurately diagnoses him with lovesickness. Romeo confesses that he and Juliet have been friends since childhood, so it couldn't be possible. May contradicts him, telling him friends can fall in love, and it is likely Beat is also in love with Illumise; Beat doesn't deny it. Romeo isn't thrilled at the prospect, treating it like a problem, but May has an idea, and asks a favor from Ash.
That night, Juliet is approached by Romeo from behind, trying to confess his feelings, but he becomes too nervous. May pops in to try and encourage him that a confession will be the best route, but Romeo isn't convinced. Ash is then revealed to be begrudgingly dressed as Juliet and acting as her stand-in for Romeo. When Romeo is unable to tell even a fake Juliet his feelings, Brock steps in to show him how it's done, but Brock winds up chasing Ash around the porch, entirely absorbed by his own emotions. At her home, Juliet wonders about Romeo's change, and why he's clumsy compared to when he was younger, and how much fun they used to have.
Outside her window, she and Illumise spot a light over the lake, which turns out to be Meowth disguised as a Volbeat, on a rope attached to Team Rocket's balloon. Once Illumise is lured over, she is netted and hauled up. On the shore, Juliet is confused, unable to see anything by the light of Illumise's bow and Meowth's tail-bulb, until they flicker out. Back at Romeo's, he's still trying to practice his confession to a dressed-up Ash, and is failing miserably. May chastises him, asking that if he likes her, then he needs to tell her. Unbeknownst to any of the group, Juliet is in earshot, hiding behind a tree and indirectly having confirmed for herself Romeo's feelings. Brock jumps up to ride on the professions, and belatedly discovers Juliet hiding. She doesn't reveal what she's heard, but asks Romeo if it was his Volbeat by the lake, and when Romeo denies it, says Illumise disappeared when they thought Volbeat had been the one. However, Romeo comes up with a plan: his Volbeat will follow Illumise's scent to track her down.
Daybreak. Over the lake, Beat picks up her scent and fly off with the other four Volbeat behind him. The humans trail them, until they hit a sheer cliff. Romeo, with a change of character, tells the others he'll climb the cliff, but the others should find another way up. Ash and Pikachu accompany Romeo. At the top, they find Team Rocket, dressed up as Volbeat and Illumise with an alternate motto to boot. They admit it was a trap, revealing Illumise hanging in a cage under their balloon-with-a-vacuum-attachment. The vacuum sucks up four of the Volbeat, and then Ash and Pikachu, who plug up the suction at the mouth. Ash tells Romeo he needs to save Illumise, and Romeo orders Beat to use Quick Attack. Beat smashes the cage, freeing Illumise. Meowth maximized the suction power, pulling Ash and Pikachu inside their containment unit, and then go after the last two Pokémon. Inside, Ash orders a Thunderbolt, which cuts the vacuum's power. Romeo orders Double-Edge, and Beat smashes the containment unit, leaving Ash, Pikachu, and Volbeat quartet dizzy from their venture. Jessie sends out Seviper to recapture the vulnerable Volbeat, but Juliet orders Sweet Scent to lure the Volbeat away. Jessie commands Seviper to try again, but Romeo calls for a five-way Signal Beam attack, effectively blasting Team Rocket off.
The day is won, and Illumise kisses her main champion, Beat, on the cheek. Looking on, Romeo finds now to be the perfect time to confess his affections. Juliet, however, acts affronted, and Brock intercedes with his own vows of love. She does turn him down gently, however, claiming there was someone else, and goes on to remind Romeo of the promise they made to get married, and asks if he's going to keep it; a blushing Romeo agrees. The following night, the May Festival performance is going well, as Romeo's confidence shines through. May attributes it to the power of love, which Ash questions, and May teases him some. The Volbeat and Illumise dance light patterns in the night sky, from a circle, to a heart, to a Pikachu.