Steeling Peace of Mind! (Japanese: ゲンとルカリオ！Gen and Lucario!) is the 110th episode of the Diamond & Pearl series, and the 576th episode of the Pokémon anime. It first aired in Japan on January 15, 2009 and in the United States on June 13, 2009.
On Iron Island, Ash's rival Barry is training with his Empoleon and Heracross when Empoleon suddenly turns on its Trainer. Barry calls Ash and Dawn, who are still in Canalave Town, to tell them what happened—other Pokémon on Iron Island are acting strangely, too! Ash and his friends catch the next ferry to Iron Island, with Team Rocket following them in secret, but Barry has already gone out to explore the island. Whatever is happening, only Steel-type Pokémon are affected, but why?
Ash and his friends search for Barry and encounter more Steel-type Pokémon running amok. Ash is even saved from an angry Aggron by a dapper Trainer, Riley, and his Lucario. Riley is a Steel-type Trainer who lives on Iron Island, and his Lucario uses its Aura to protect itself from the low-frequency wave that's driving other Steel-type Pokémon mad. Barry and his Heracross, off on their own investigation, spot a strange machine. Barry runs into Team Rocket and promptly blames them for everything, but Team Rocket denies that the machine is theirs. Barry and Team Rocket go to get a closer look, and discover that the machine is part of a Team Galactic operation headed up by Commander Mars!
When Team Galactic spots them, Barry and Team Rocket put up a fight but are quickly overpowered and knocked into an ancient underground ruin. Up on the surface, Riley and our heroes have also tracked Team Galactic to the ruins, which are made of metal. Together with Team Galactic's Spear Key, this must be causing the low-frequency wave! Commander Mars releases the Spear Key and the Key melds with the ruins, which release a huge bolt of energy. The wave of energy knocks Lucario backwards; as it gets to its feet, it's overcome by a strange power and prepares to attack!
As Barry practicing on Iron Island, Heracross and Empoleon destroy a rock. Empoleon gets hit by some sort of electricity which later turns out to be a low frequency sound wave. It then starts to attack Barry and Heracross. Meanwhile, Ash, Dawn and Brock are getting prepared to leave Canalave City to head to Dawn's next Contest. Before they leave, Ash receives a call from Barry asking about how his training is going. Ash tells him about his win at the Canalave Gym. Barry is at Iron Island, and something is currently wrong with his Empoleon and some other Pokémon who've begun to act violently. Nurse Joy explains that she can't figure out why this is only happening to Steel-type Pokémon.
They take a ferry and go to Iron Island but when they get to the Pokémon Center, they find out that Barry has already left. While exploring the island, the group find that all the Steel Pokémon are trying to hurt them and themselves. Suddenly, a huge Aggron comes up to them and is about to attack them when a man called Riley comes in to save the day and his Lucario gets rid of the Aggron. Lucario can use his aura to detect the waves and find out if there are any rampaging Steel Pokémon nearby, although he will not be affected because he can also use the aura to protect himself from the waves.
Team Rocket, who followed Ash and his friends to the island, have a run in with many of the rampaging Steel types before Barry and his Heracross fall onto them. He accuses them of angering the Steel types, pointing out a device he spotted in the air but Team Rocket claim it was none of their doing. He leads them to the location, which turns out to be a Team Galactic base led by Mars. They try to fight Team Galactic with their Pokémon but it doesn't work. They then fall through a crevice into a small cave with Dialga and Palkia etchings.
Ash and friends finally reach the base with Lucario's help. Eventually Mars picks up a key and inserts it into a slot into the ruins on the island and a powerful radio wave is sent out. Even Lucario can't fight the disturbance any more, and is about to attack the group while Ash and Riley try to calm it down.