2013. A young boy and his family are picnicking when they look up and see massive alien spaceships enter Earth's orbit. The boy stands, shocked and transfixed.

2046: It's a story as old as time: A young woman is super mad at her father. But there, the story changes, since Nolan is human and Irisa belongs to a race called Irathients, part of the Votan cadre of aliens who arrived on Earth and transformed it to something completely different. As they tumble through a post-apocalyptic landscape, Irisa is writing in her journal in some freaky alphabet, saying her dad's plans turn to "shtako," the coolest fake swear word since "frak" (The only fake swear word since "frak"? Probably.). The Johnny Cash song "Jackson" comes on the radio, saved by the Post-Apocalyptic Society for the Preservation of Cool. Nolan and Irisa are hunting fallen pieces of space junk from the wrecked ships of the long-dead intergalactic war that brought alien races to Earth and made them native. There's a payload straight ahead, and when they reach the ship (or "ark", in the new world's lingo), there's a cool, glowing soccer ball-thing that's worth top "ja-ja" to the Earth Republic. When they sell it, they'll be rich.

But their celebration is cut short when Nolan turns to see Irisa held at gunpoint by Spirit Riders, a Mad Max-style gang of Irathients – Irisa's race. They're after the soccer ball (really called a terrasphere). They're about to take everything the small family has when Irisa pulls a ninja knife move, allowing Nolan to get free and the two to make their getaway. Too bad Irisa gets shot in the process.

Nolan carries the wounded Irisa through woods infested with some kind of spider-wolf hybrid. He sets her down and buries the sphere for safekeeping, then draws his piece as several of the alien monsters approach. Nolan empties his energy bullet-clip, but the beasts keep coming until a stranger arrives and scatters them. He brings them to the nearby town, of which he is Lawkeeper, to recover. Nolan sees the giant arch in the center of the town. "Is this St. Louis?" he asks. "It used to be," says Lawkeeper Clancy. "Now we call it Defiance." The view of the pioneer city is as epic as a title shot should be.

Once Nolan's out of Doc Yewll's (an Indogene, one of the alien races) sick bay and convinced Irisa's in good hands, it's time for him to meet the Mayor, Amanda Rosewater. She's three weeks on the job - her beloved predecessor, Nicky Riordan, has gone into retirement (but is still feisty, as we see). Amanda just wrapped up an address to the town – crumbling and being built grander – to kick off the celebration of the day of armistice, and the "defiant few" for which the town was named. The party is sponsored by the two big families of the town, the Tarrs (a Votan race called Castithans) and the McCawleys (plain ole' humans). The patriarchs, Datak Tarr and Rafe McCawley are clearly rivals, but it seems the youngest progeny - Alak Tarr and Christie McCawley - have a little Romeo/Juliet thing going on.

The fact that Nolan was one of the defiant few doesn't buy him much purchase with Amanda, who's worried about human/Irathient relations and wants him and his daughter (adopted, war orphan) to clear out. They'll need money to do that, and Kenya, the owner of the NeedWant (the local brothel/bar), tells Nolan that he can earn some quick scrip in The Hollows at a bare knuckle fighting ring. When he enters the ring, owner Datak – who looks every bit the villain with his glossy white skin and severe features – substitutes the champion for a bioman. Just as it sounds, bioman = super-muscled android built to kill. Nolan barely manages to punch the bioman's off switch, but celebration is once again cut short when Datak calls him out on his low blow. Tarr leaves them with only enough cash to clean up and head back to the brothel, where Nolan gets biblical with Kenya.

They get out of bed just as Rafe blazes into the NeedWant seeking vengeance on Alak Tarr for killing his son, Luke, who tussled with Alak after seeing him dance with younger sist Christie. Luke was killed with a cold fire blade, a weapon brought by the Votans, and Christie's confession that Alak couldn't have done it because he was with her only gives Rafe more reason to shoot the boy. Irisa and Nolan knock weapons out of hands and heads against tables faster than you can say dynamic duo, but in the melee, someone shoots Lawkeeper Clancy, and he falls dead.

Penniless again, Nolan drops that he's a tracker and accepts Rafe's pay rate of 20,000 scrip to find the real killer. Soon, he discovers that the killer is an Indogene – a partly cybernetic Votan race – with a left leg injury. Amanda's assistant, Ben, matches this description. What do you know? Ben is just at that moment in the middle of killing a guard in order to lower the stasis net that protects Defiance from outside threats.

Nolan and Amanda chase down Ben in a car, with her snarling at him and him calling her sweetheart. He says "sweetheart" was his second choice (what was his first? Princess?) In a violent interchange with Ben, they learn that the Volge, a race of alien soldiers, is heading to Defiance, and without the stasis net, they'll be crushed.

Amanda prepares to rally the town to action, and the words of Kenya (her sister!), give her the boost she needs. Nolan's surprised to learn they're sisters (do I smell a love triangle brewing?), but Amanda's speech strikes a chord in him. Later, as he exhumes the soccer ball, he considers his options. The Indogenes in Defiance have the ability to make the thing into a bomb, but Irisa's having none of it. She leaves him to fend for himself. Nolan returns to a town unified under Amanda – even the McCawleys and the Tarrs fight as one – and Doc Yewll tells them to keep the Volge in the valley pass while she configures the sphere into a bomb.

The Volge fire on the scaffolding where the doc works and it looks like the battle may be lost, but Yewll regains her footing and Irisa appears with the band of Spirit Riders from the first scene to fight along. Yewll releases the bomb and the Volge are destroyed! Nolan and Irisa reunite, and Datak allows romance to bloom between Alak and Christie, thanks to his wife Stahma reminding him a marriage between the two gives them access to the McCawley mines and money. Nolan accepts Amanda's offer to be the town's new Chief Lawkeeper, and it's not just because St. Louis is his hometown – the first place that he saw the Votan ships in the sky as a boy of ten (that kid in the beginning! It was Nolan!). But it's mostly because of that.

We end with ex-Mayor Nicky conspiring with a man named Birch. First, she's smoking indoors which clearly means laws are looser in 2046. Second, turns out NICKY is behind the Volge attack and promises to do something even bigger and badder to achieve her goals. But what are they?