It's Darington's birthday, and Crusher's attempt to steal his birthday cake causes it to fly away, and Blaze and AJ have to catch it before Crusher does.
The episode begins at the Axle City Garage, which is decorated. AJ and Gabby explain to the viewer today is Darington's birthday and they're getting the garage ready for his party. Darington is excited and knows it'll be the best party ever, but when he tries to present the birthday cake all there is an empty pedestal. Darington becomes sad, thinking his party is incomplete without a cake, but Gabby tells him the cake is at the bakery, which cheers him up. Blaze and AJ offer to pick up the cake while Darington and Gabby finish decorating which he gratefully accepts, and Blaze and AJ take off.
Arriving at the bakery, Blaze and AJ meet Clive, who presents the birthday cake to them. The cake is the biggest ever seen, and smells delicious. All it needs are candles, so Blaze and AJ go inside to find some.
Unbeknownst to them, Crusher and Pickle are coming up the road, the latter singing everything he sees. Crusher is unamused, but when Pickle sees Darington's cake, he immediately perks up and wants to eat it, unaware of who it belongs to. He constructs a flying robo-plate to pick it up for him, but since it goes really slow, he tries to get it to fly faster but ends up breaking the remote, causing the plate to fly out of control.
Crusher and Pickle chase the cake, just as Blaze and AJ are coming out of the bakery with the candles. When they see the cake fly past and Crusher chasing it, they realize he's trying to get it despite the fact it's for Darington. Blaze announces they have to catch the cake first, and hurry after such as Burn Rubber is heard.
The cake flies down the city streets, and as Crusher frantically tries to follow it, Pickle comes forward with some mail that is addressed to them. He asks Crusher to open it, but he refuses due to not having any time for that. When they hear Blaze and AJ, Pickle concludes that Blaze wants the cake but Crusher is determined not to let him get it. So he sends out bumper bots which bump him away.
Blaze points out there's only one way to get past the bumper bots: they have to bump them away even harder than they do. AJ decides to use kinetic energy - the energy something has when it's moving. As Blaze charges for the bumper bots, he speeds up accordingly with help from the viewer and manages to bump all of them away. He and AJ then sing a kinetic energy song as they pass through the amusement park and try it out.
Crusher is still chasing the cake with a butterfly net, and Pickle has once again showed him the unopened mail which he refuses to open. When he attempts to catch the cake, he misses it and catches a woodpecker instead which pecks him all over.
As Crusher enters a tunnel, he hears Blaze's horn and panics, and builds a wall to stop him from following him. Blaze concludes only a powerful machine can break it - a crawler crane with a heavy wrecking ball. Transforming into one, he swings with enough kinetic energy from the viewer's help and breaks down the wall. They continue on, but they have to hurry as Darington's party is going to start soon.
Now in the forest, Crusher is still desperately chasing the cake and again refuses to open the mail Pickle gave them. He attempts to grab it with a fishing pole, but again he misses and gets the pecking woodpecker instead.
When he sees Blaze coming yet again, Crusher makes a super slippery ice machine to ice the ground, making it too slippery for Blaze to drive on and cannot move. To get across, he needs someone with kinetic energy to bump him forward. Blaze then spots a bighorn in the forest, and since bighorns love bumping things, he asks him to bump him. The request works, but it wasn't enough for him to get all the way across. Blaze has the viewer find more bighorns for him, and with that, he makes it to the cake and gets it back.
Crusher is upset he didn't get the cake, and Blaze reveals to him it's for Darington. Crusher apologizes, revealing he would never touch someone else's cake in the first place, but he still wants to have it. Crusher then agrees to open the mail Pickle gave him, and to his joy, it's an invitation to Darington's party. But the party is about to start, so Blaze uses Blazing Speed to get them back to the garage in time.
Returning to the garage, Blaze puts the cake in its proper spot, and all the guests arrive. Darington welcomes them in and starts his party, and soon it is all underway. Darington thanks Blaze for making this his best birthday ever, and everyone wishes Darington a happy birthday, ending the show.