Ash, Misty, and Brock are taking a rest in a valley before Ash goes up against his next Johto League Gym. While the three rest, a wild Sentret stumbles upon them and reports what he saw back to the other Sentret. On a more restless note, Team Rocket is planning on testing out their new Arbo-Tank (a tank resembling Arbok) by stealing Pikachu as the twerps sleep, but as Meowth points out, if they were to roll up to the twerps in the Arbo-Tank, it would wake them up, so the three have to get out and walk.
While Ash, Misty, Brock, Pikachu, and Togepi sleep, the Sentret comes back and tries to figure out what Togepi is, but in the process, the fast-asleep Togepi rolls down a hill, and the wild Sentret chases him. At the bottom of the hill, Togepi wakes up and meets the Sentret. The two play together and end up rolling off a cliff, but they fall into the Arbo-Tank's opening. The two play with the control panel and figure out how to drive it, and when Team Rocket sees this, they chase after them.
Misty is the first to wake from the nap and notices that Togepi is gone; but before she can wake up Ash, a Sentret comes along and wakes him. The Sentret tries to desperately tell him something, and Brock suggests that it's trying to find something it has lost. Then, the trio hear a crash coming from the distance. The crash came from Togepi and the Sentret trying to navigate around a rock, but once they do, they crash right into the side of a cliff.
Both Ash, his friends, and Team Rocket chase after the tank, and soon, the two groups meet up. Team Rocket tells Misty that Togepi is inside controlling the tank, and this sends Misty running for the tank again. Meowth then tells the Sentret that is with Ash's group that there's also another Sentret in the tank, which sends the Sentret right after Misty. Brock sends out Onix so they can get to the tank faster. They get to a clearing that the Arbo-Tank should be passing by soon, and devise a plan:
Onix will dig a hole in the clearing, they'll fill it with rocks and crush those rocks to dirt. They will then use water Pokémon to turn it to mud, and the Arbo-Tank will fall into it and get stuck. Then, Ash, Pikachu, and their Sentret will enter the tank and rescue Togepi and the other Sentret.
The Arbo-Tank gets there before they can completely turn it to mud, but it falls into the half-filled hole. Pikachu, Ash, Misty, and the Sentret rush to help rescue the two, but as they begin to climb inside, the Arbo-Tank is able to return to a standing position, and only Pikachu is able to get inside. With a rocket, Togepi blasts the tank out of the hole and continues on the accidental rampage.
Dressed as magicians, Team Rocket appears and says they have a trick to show, and suddenly, the Arbo-Tank disappears. Ash and his friends rush to see what happened to it, but when they get there, they see that the tank has fallen into another hole, this one which Team Rocket dug. Meowth jumps into the tank, only to be greeted with Pikachu's ThunderShock. The shock causes a technical failure with activates a spring on the bottom of the tank, bouncing it out of the hole and away from Ash.
While the tank is smashing its way through the cliffs, Sentret calls to signal for danger so other Pokémon will know to hide. The tank starts going faster and is about to crash into the side of a cliff, but Togepi uses Metronome to drill a hole through the mountain. Brock concludes that if it drills straight through the mountain, it will destroy a town on the other side, and no natural obstacle with overcome it, so they need to use Charizard to defeat it.
Charizard is able to bring the tank to almost a halt, but needs help to completely stop it, so the Sentret helps along with Pikachu who uses a ThunderShock on the inside to cause a complete mechanical failure, and Onix grabs onto the Arbo-Tank's tail. Charizard uses Flamethrower to melt the window and free Pikachu, Togepi, Sentret, and Meowth, but Meowth doesn't get out, while Jessie and James try and rescue the Arbo-Tank at the last second, but the Arbo-Tank explodes, sending them blasting off again.
The episode ends with the two Sentret being reunited and Officer Jenny telling them that the tunnel that the Arbo-Tank made would cut driving time from the local town to Violet City in half.