Sparks fly at the annual Ironwood Firefly Festival. Caitlyn decides to take a leap of faith. Zac jumps the gun on his mission to race Harris Bowers. Marcel unveils his signature logo. Curtis is pulled into the seedy world of his brother, Ray. And Uncle Logan is presented with an opportunity.

Urged by Logan to repair his friendship with Marcel, Zac suggests they go to an unreasonably dangerous Go-Kart track. Curtis invites Caitlyn to a family BBQ, where a surprising guest joins them. Harris prepares for an upcoming street takeover. Sam discovers how much Ironwood has changed, while Logan reminds her that the best parts of Ironwood will always be there.

Zac and Curtis skip school together and watch some high octane drag racing at an abandoned air strip, run by Curtis' brother, Ray. Kiara invites Caitlyn to lunch, which turns into a group outing. A video of Harris Bowers' street takeover is mocked online, leading to an exhilarating street race. Zac asks Logan to train him, just like he taught his brother, Zac's dad, years ago.

Car auction in Ironwood. A nostalgic Sam considers bidding on her old car. Marcel convinces his dad, Wade, to make his famous chili. Logan takes Caitlyn's advice and starts a car restoration side gig. Zac has a secret street race. And realizing everyone else has a spot, Caitlyn finds hers.

Marcel gets bad news about his dad, so the crew takes him to White Knuckle Run, an ATV dirt motocross event in nearby West Newton. Logan and Sam take a road trip to see Marcel's mom. Sheriff Hugo Young enlists Ray's help finding some local criminals. Harris challenges Zac.

With only three weeks until Zac's race with Harris, the crew works overtime to finish the UNB10 car. Zac's confidence grows with Ray's guidance. Caitlyn and Curtis discover a possible clue to Christian Maddox's whereabouts. Logan discovers who Zac's been training with. Harris faces a new challenge on his mom's birthday memorial. Curtis takes Brooke for a ride on his bike.

Homecoming. Marcel and Brooke's post-apocalyptic themed dance is a big hit. Zac hopes to meet up with Alicia. Hitting an electrical snag with the car, Caitlyn and Curtis wonder if they should skip the dance. Sam and Darren Bowers co-chaperone, looking out for “commotion.” Kiara is fed up with Noah. And one of the bank robbers from 17 years ago gets out of prison.

It's time to turn the key on the UNB10 car, but will it start? Zac gets a big race at the speedway, but with an unexpected opponent. Ryan asks Harris to meet someone. Brooke and Curtis grow closer. Logan and Hugo are out of options. Marcel and Brooke become “friendly” rivals.

UNB10 is ready for the big race, but is Zac? Caitlyn visits Buzz at the junkyard, wondering what's next for her. Marcel takes a leap of faith. Brooke prepares for her winter break. Curtis confronts his father. Logan attempts to get out of Ezra's plan. Kiara stands up to her mom. And Harris, feeling lost and alone, reaches out to Alicia.