In a dark alley, a large, talking rat named Argit sees a normal-size rat scurry along the ground, so he shoots it with his laser gun and eats it. Afterwards, Kevin drives by and meets with him, since they're both old friends. Argit says he's been waiting for him for an hour, and Kevin wants to hear what Argit's proposition is. Argit tells him that he's got the tech Kevin's been looking for. However, since Kevin is reluctant to trust Argit, Argit doesn't feel like helping Kevin anymore and starts to walk away. But Kevin follows him and tries to convince him to make a deal with him. Argit, though, doesn't have the actual weapon, but promises Kevin to make a connection with the person who does, and that it's going to cost Kevin.

While Kevin works on fixing up the Rust Bucket, Ben and Gwen look at an old photo of when they were 10 years old, spending the summer with Grandpa Max. Ben remembers how he used to "go hero" all the time back then, as well as when Kevin used to be a bad guy. Gwen puts the photo back in the box she got it from and wants to take it back inside the Rust Bucket, but Kevin stops her, saying it's not ready yet. And Ben jokingly says he's still not buying Kevin's "nice guy" act.

Inside the Rust Bucket, Kevin uses his Plumber's badge to open up a secret panel on the dashboard and tells Ben and Gwen that he's going to try the engine and turns the key. Ben congratulates him on getting it to work, but afterwards, Kevin puts the Rust Bucket in drive and starts to drive away with it. Ben calls out to him to get him to stop and uses the Omnitrix to transform into a new alien, Big Chill. As Big Chill, he flies after Kevin. Kevin sees him coming through one of the mirrors and presses a button on the dashboard to activate a laser gun at the top of the Rust Bucket to start shooting at Big Chill.

Big Chill is able to avoid all the lasers and uses his ice breath to freeze part of the road to force Kevin to stop, but Kevin activates the spikes on the tires to be able to drive on the frozen road. So Big Chill uses his ice breath once more to throw the Rust Bucket off the side of the road and into the woods below. Kevin is then able to make onto another road, with Big Chill still chasing him. Big Chill uses his invisibility power to make himself invisible to Kevin, but Kevin uses the Rust Bucket's net missiles to capture Big Chill in a net so that he can escape.

Ben returns to normal and Gwen catches up to him using her magic. Ben tells her that Kevin got away and that he's a liar and a thief. But Gwen tells him that that was the old Kevin and that he's different now. Gwen says that she can still track down Kevin using his handkerchief and her magic. Elsewhere, Argit examines the Rust Bucket's engine and tells Kevin it's just a bucket of bolts. So Kevin takes him inside to and shows him some of the Rust Bucket's secret compartments. Argit tells him the aftermarket extras are worth a lot and that the guy he works for would take it... if he ever got the chance. Argit decides to betray Kevin and shoots the quills on his back at him, paralyzing him.

Argit tells Kevin that the Rust Bucket will help pay everybody he owes money to and still have some left over for himself. He throws Kevin out of the Rust Bucket and tells him the tech dealer is named Vulkanus and that he wants him dead. Afterwards, Argit drives off with the Rust Bucket. Kevin uses his absorbing powers to absorb some of the rocks on the ground so that he can move again. He tries throwing a huge boulder at Argit before he can get away, but Argit dodges it and continues his escape.

Afterwards, Ben and Gwen catch up to him, and Ben is furious at Kevin for losing the Rust Bucket and wants him to get it back. Kevin uses his Plumber's badge to activate a holographic map, since he planted a tracking device on the Rust Bucket's undercarriage beforehand. They use Kevin's car to go to the location indicated by the Plumber's badge. They reach an old warehouse and find the Rust Bucket. However, it's already been stripped of all its Plumber tech. Ben is mad that they're supposed to be protecting Earth from an alien invasion, yet they can't prevent a motor home from being stolen.

They hear someone trying to open the door, so they all hide. Argit is the one who enters and goes inside the Rust Bucket to retrieve a piece of Plumber tech that he missed before. However, before he can leave, he's confronted by Gwen, Ben and Kevin, so Argit jumps out the window to make a run for it. So Ben transforms into Echo Echo and uses his sound wave to attack Argit and surrounds him. But Argit uses his quills to defeat Echo Echo. Gwen then arrives, and Argit is about to fire his quills at her, too, but Kevin pushes her out of the way. However, they both end up getting hit with a quill on their back, knocking them both unconscious.

Echo Echo is still able to fight, so Argit prepares to fire his quills again. But this time, Echo Echo is ready and uses his Wall of Sound technique to redirect Argit's quills back to him, leaving Argit unconscious. When he wakes up, he finds himself tied up and unable to use his quills, since Echo Echo tells him he superglued them to his head. Echo Echo asks his clones if they're all awake, but one of them is still asleep due to one of Argit's quills getting stuck in his back. Echo Echo says it's close enough and the clones all jump on top of him so that Ben can return to normal.

Argit tells Kevin that he cannot trust Vulkanus, as he was planning to sell the Rust Bucket to another criminal. Ben calls Kevin a thief for always being up to something. Kevin becomes angry and tells him he doesn't have to explain himself to him or to Gwen and leaves. He goes off to see Vulkanus on his own, since he heard he wants to see him. Vulkanus is angry at him for the counterfeit-isotope incident a while back, where Kevin left him at the mercy of the Plumbers. Kevin tells him that's all ancient history now and wants to make a deal with him.

Vulkanus tells him he has the Plumber gadget he wants and shows it to him. He asks him what he wants to trade for it, but Kevin tells him he doesn't have the Plumber tech he was going to give him, so he wants Vulkanus to tell him what he can do to get it. Vulkanus thinks about it and forces Kevin to absorb a piece of Taedenite (Diamond Head crystal), the rarest gem in the galaxy, to pay him back for the double-cross. Vulkanus forces Kevin to continue absorbing the crystal until his whole body is covered in Taedenite.

Vulkanus' minions begin to chip away at the large Taedenite spikes on Kevin's back to collect them so that Vulkanus can sell them off. Vulkanus tells Kevin that he's going to continue doing it forever. Kevin doesn't care what he does to him, but he wants Vulkanus to give the holoviewer to Ben. However, Vulkanus tells him he's not in a position to make demands, since he's all alone. But Big Chill and Gwen reveal themselves inside Vulkanus' hideout and tell him Kevin is their friend.

Vulkanus fires his flame gun at Big Chill, sending him flying into a pile of debris, while Gwen uses her magic to defeat his minions. As Vulkanus goes to check on Big Chill, he sees him trying to attack him from behind and fires his flame gun again, but this time, Big Chill uses his ice breath to push back the flames. Since his weapon didn't work, Vulkanus tries to punch Big Chill directly, but But Chill uses his intangibility to prevent Vulkanus' punch from hitting him, making him hit the ground instead and break his hand.

Vulkanus tells him he wouldn't even be fighting him if Big Chill knew what Kevin did to him. But Big Chill tells him that he already knows that Kevin steals and runs away, as that's who he is. While Big Chill is talking, Vulkanus squirts some of the oil leaking from his broken hand into his Big Chill's eyes and punches him away. Meanwhile, Gwen manages to defeat all of Vulkanus' minions with her magic.

Vulkanus grabs Big Chill and tells him that he's the injured party and that the Plumbers blew up his ship. Big Chill uses the opportunity to use his ice breath to free himself of his grasp, and then uses his intangibility and freezing powers to freeze Vulkanus from the inside out and shattering his body, leaving him with only his head and a miniature body and runs off. Afterwards, Gwen frees Kevin and uses her magic to return him to normal. Before they all leave, Ben asks Kevin what they should to about the miniature Vulkanus, who's playing with a pile of Taedenite crystals, and Kevin says to leave him alone, as they're now even. Kevin picks up the holoviewer that was left on the ground and gives it to Ben. He tells him that one is special. Ben asks him why he didn't tell them about it. Kevin replies that he's an ex-con, and that he's done a lot of stuff he's not proud of. If they knew, they probably wouldn't trust ever again.

After the three of them have resolved all their issues with each other, Ben activates the holoviewer and finds that it's a message from Grandpa Max. In the recording, Max tells Ben that he can't go at it alone and that he needs to continue finding more of the Plumbers' kids and put together a team.