As the sun shines brightly on another fine day in Kalos, the Vaniville group has finally made it to the end of Route 4, also known as the Parterre Way. Ever since their encounter with Korrina, the 5 young trainers have been in high spirits, but out of them all, Trevor is certainly the one feeling most elated. Finally, he has learnt of the actual names of the two stones related to Mega Evolution: the Mega Stone on the Pokemon's side, and the Key Stone, which is the seven-coloured rock embedded in X's bracelet, on the trainer's side. For Korrina, her Key Stone was set in a glove instead of a bracelet, which suggests that there are many possible ways for one to wear the ornament, but it confirms that an interaction between the two stones are the basis for Mega Evolution to happen.

Trevor contemplates on the hypotheses he has made on Mega Evolution so far, and steals a glance at Kanga, wishing that he could test another theory. For some reason, X catches Trevor's thoughts even despite being inside the tent, and asks if he is thinking of experimenting on whether Pokemon other than Kanga also trigger the same phenomenon if they are given the Mega Stone to hold. Trevor laughs sheepishly that X has really sharp senses, but to his shock, X actually agrees to the experiment, which also astonishes Y, Shauna and Tierno.

X believes that they will arrive in Lumiose City after passing through the gate ahead, and thinks they should just do it right here. He steps out from his tent, and Trevor is thrilled about X's proactivity. The orange-haired boy decides to start with Chespin, and borrows Kanga's Mega Stone to give it to the spiny nut Pokemon. X places two fingers on his Key Stone to activate it like he did with Kanga, but after a while, nothing seems to happen.

Trevor realizes that things aren't as simple after all, and wonders if it is because Chespin is not a species that could Mega Evolve. On a deeper thought, he thinks it might be due to the fact that Chespin still doesn't belong to X officially, and decides to persuade X about it again. However, before he could finish his sentence, X strictly declines and retreats into his tent. He reiterates that it will not do the Pokemon any good to join his team, and Y is frustrated about X's stubbornness on the matter. Shauna, on the other hand, thinks the problem may lie in how Chespin feels, and notices that Chespin seems to be distracted by something.

It turns out that a Charmander is sleeping in a nearby flower field, and Y sees that Froakie's attention is apparently drawn to as well. Suddenly, the sleeping Charmander falls to its side and the flame on the tip of its tail sets the grass on fire. In a blink of the eye, it breaks into a huge blaze, causing everyone to cry out in shock. Charmander runs around in circles as it panics, and Shauna exclaims that it will only make the fire spread quicker. Froakie foams up a giant cloud of frubbles, and hurls it towards Charmander and the flower field, successfully putting out the fire. Everyone is impressed by Froakie's work, and Charmander wipes a sweat off its forehead as it plops down onto the floor.

Chespin and Froakie approach Charmander merrily, and Tierno sees that they seem to have become friends. However, Shauna notes that they seem more than just friends who just met, and Y agrees that they certainly look more acquainted than strangers who just helped each other out. Trevor suddenly thinks of something, and soon recalls that he actually saw this Charmander when he was speaking with Prof. Sycamore through the Holo Caster. He rationalizes that the three actually knew each other when they were at the Professor's lab, and his guess is confirmed by the smiling faces of Chespin, Froakie and Charmander. Trevor then gets an idea, and picks up Charmander, fervently asking X to try Mega Evolve it. Y stops him and cries that he is too persistent sometimes, and Shauna even scolds him that he may make X refuse to come out from now on. Trevor apologizes embarrassedly, and Tierno suggests they check out the photos from Viola again.

Nearby, on the top of the gate walls, a young man and young woman wearing scarves and masks are spying on the group. They see Charmander tagging along the group as they head for the gate, and mutter among themselves that they have spot their target.

As the Vaniville kids step through the gates and arrive in Lumiose City, the sight in front of their eyes causes them to gap their mouths wide open in awe and bewilderment. In every direction, the streets just seem to go on forever, and the sheer size of the city makes it impossible to see the other end. Every alley is lined with cozy cafes or specialty stores, and there are tourists in basically every corner of the city. The group passes by a Furfrou styling salon and a dance studio, and both Shauna and Tierno sigh that they would probably be over the moon if they came here to pursue their dreams. Unfortunately, it is not the case. Y sees her friends' sad faces and feels upset, but couldn't think of anything appropriate to say to comfort them.

Trevor is still trying to take in just how big the city is, and wonders where they should go. Y holler in bewilderment at his remark, and wants to know what he means by that. Trevor reveals that he has actually never met Prof. Sycamore in person, and thus has no idea where his Science Lab is. His answer causes Y, Shauna and Tierno to shriek in unison and Y feels completely confused as to how Trevor received Pokemon from a person he never met. Shauna goes frantic and demands to know how exactly they knew each other, and Trevor urges them to calm down to hear him out.

It turns out that it was a coincidence that Trevor and Prof. Sycamore crossed paths. Some time ago, for his own learning, Trevor yearned to read an article written by a scholar in a distant region few years back. Unfortunately, despite having searched through various libraries, he failed to find it. He started searching online and asked about it in bulletin boards, and one fine day, a user named Sycamore wrote a reply and claimed to own a copy of the article, which was titled '90% of Pokemon is tied with evolution'. Trevor and Sycamore then exchanged Holo Caster numbers to chat in person, and that was the first time the two made contact. Sycamore revealed that the article was written by his teacher, and was pleasantly surprised that someone as young as Trevor knew about it. The two became acquainted afterwards, and often discussed on matters with each other.

Shauna believes that Trevor must have also asked for his advice on how to help a friend who has locked himself up in his room for years, and Trevor admits it with a grin. Y now understands why Trevor doesn't know where the man lives, and wonders what they should do. At that moment, X suddenly speaks up and queries if they can really trust the Professor. He states that ever since they set out, they have been attacked on every path they took and every facility they entered. He hopes that none of his friends actually think that Lumiose is any different. Indeed, Y, Shauna, Trevor and Tierno hardly consider themselves safe in this city, and all become silent.

X decides that he will stay where he is and tells the others to figure out what they want to do. Y gets upset and says they are obviously not okay with such a plan, since X has been the key player in all the problems they encountered so far, something which he should know himself. X mutters that they are free to go find the Professor if they think he is trustworthy, and Y reminds him of rule 5 of their pact: never leave your friends' side and all 5 people must always be together. However, X retaliates with rule 1: do not follow strange adults, and Y instantly breaks into a fury, arguing that Trevor knows the Professor and they can decide whether they can trust him when they meet. She gets ready to kick around like she always does, and Trevor quickly pacifies her.

Suddenly, the two masked trainers who have been spying on the group reveal themselves and demand they return the Charmander they stole. The two hop towards the little fire lizard, snatch it up before anyone could react, and begin to dash off into the distance. Tierno fumes with rage for being accused to theft, and begins to give chase after kicking on the Roller Skates Korrina gave him. Speeding past the two trainers, Tierno does a Parallel Swizzle, jumps into midair and gracefully lands after snatching Charmander back from the female trainer's arms as he somersaults past her. The two trainers exclaim at Tierno's agility, and Shauna states that they are dealing with a professional dancer. Tierno clarifies that they did not steal Charmander but it followed them, and the two trainers immediately apologize for their mistake.

Later, at Prof. Sycamore's Science Lab, the man is relieved that Trevor and his friends have arrived and says he has been worried sick since the Vaniville incident. He thanks them for bringing back the Charmander who escaped from the lab a few days ago, but Trevor blushes that they didn't really do much. Sycamore mentions that there has also been a blackout in the city recently, which caused quite some trouble, and feels grateful that they are alright. He believes that their group must have gone through a lot, and tears start to well up in Trevor's eyes.

Sycamore knows that they have been debating on whether to trust him or not, and both Sina and Dexio, who are actually the masked trainers, keep themselves hidden and hope the kids wouldn't mind them telling the Professor about it. Trevor feels embarrassed and doesn't know how to reply, but X outright admits it, and says everyone apart from Trevor knows nothing about Sycamore. The Professor sees what X means, and also believes it is probably the reason why they didn't accept the Pokemon he sent over. He can tell that neither Froakie nor Chespin has been taken up by anyone, but X states that it is another issue. He scoffs that Pokemon will suffer if they join his team since they will get chased and attacked constantly, and Trevor tries his best to calm X since he can feel him getting defensive about the matter again.

However, Sycamore states that while he doesn't doubt what X said is true, he wonders if the boy ever thought that he has the ability to change himself. The young professor believes that there is a solution to everything, and points out that X has the choice to make himself a man who is worth staying with despite being chased and a man who makes one feel secure despite being attacked. His words instantly make X speechless, and the boy finds himself unable to argue back despite feeling disgruntled.

Sycamore grins that if words cannot convince him, he shall do it with a battle, and tells X to fight his Charmander with Chespin. X protests that he only battles with Kanga, but Sycamore states that since he made the invitation and it is his lab, he gets to decide on the rules. The man starts scribbling the battle regulations on the board, basically outlining a 1 on 1 single match, and Shauna marvels at his great penmanship. Sycamore giggles that he should first declare that he is not a strong battler, but thinks there is something about the mind that he can teach X about. He then turns to Trevor, and tells him to get the Holo Caster fixed meanwhile so as to make good use of their time. He instructs them to find a red café on the northern side of Lumiose, and says he has already contacted the person who will repair the device for them beforehand.

Trevor, Y, Shauna and Tierno make it past the huge tower in the city center according to Sycamore's directions, and manage to locate the café on their left. They are seated by the waiter who then goes off to inform the Holo Caster repairer of their arrival, and Trevor suggests looking through Viola's photos while they wait. While at the Santalune Gym, they have sorted the photos into four groups: one on the winged Pokemon, one on the huge antlers Pokemon, one on the collapsed building, and one on the people who were fleeing. However, they haven't learnt any further information beyond what the photos already portray, and Trevor wonders if it is because the scenes are too painful to look at and they are subconsciously avert their gaze from their details.

Y notes that one of the photos is set aside from the four groups and wants to know what it is. Trevor states that it doesn't really belong to any group, since it depicts a silhouette amidst the smoke and dust. Shauna thinks that it resembles a human being, and Tierno says there is a chance that it is one of the enemies.

At that moment, the Holo Caster repairer arrives to greet them. Trevor turns around to see a man in black leather with fiery red hair and beard, and his face instantly turns white. Trevor has always wondered if perhaps when humans have powerful thoughts about something, they would naturally be drawn to a direction or something that is related to it. The man extends his right arm and offers to fix their device right away, but Trevor finds himself trembling with fear. He steals a glance at the photo he holds, and it is apparent that the Holo Caster repairer strongly resembles the silhouette in the photo.

And so, while X is fighting a match that he is uncomfortable with back at Prof. Sycamore's Science Lab, Trevor also finds himself battling a different kind of terror.

Meanwhile, in a forest elsewhere, Xerosic feels astonished, and looks at up the giant barren tree that he has found. He remarks that he actually didn't expect to find it at such a place, but then wonders if it is still appropriate to speak to it as if it is still a living creature. After all, it breathing and circulation have stopped, and it has turned into its dormant state as the legend says. However, he finds himself lucky to discover it as a tree, and addresses it as Xerneas…