Short au fic, based on a misunderstanding of the timeline before I read the comics. Kon and Bart are dead before Chemo — the bomb — is dropped on Bludhaven. More notes at the bottom.
Only take what you can carry.
..
She's helping the emergency workers load people into the ambulance when she sees it.
High above the city, the Brotherhood of Evil's ship hovers. It's been there for hours, as the threats played over the radio. Supposedly Nightwing was taking them on. Or maybe Black Canary, somebody who kept the looming threat at an impasse. Whoever they are, they failed, as the ship makes its first move in hours. The bay doors swing open. Out falls an object, no more than a winking green speck from this distance, plummeting towards the distant skyscrapers.
Cassie knows a bomb when she sees one.
There's no catching it, let alone disarming it. Maybe if Bart was still here, they would have a chance. But he isn't, and at the moment the city is sorely lacking in speedsters.
There's no stopping the bomb.
Cassie's grip slackens on the woman in her arms. She feels the hands clawing at her shoulders, her wrists, the people crowded around her desperately grabbing for her clothes as they realize what's about to happen. She rises, feet leaving the ground, and they lose their grip, falling back to the shattered concrete. Their helpless cries sound muted under the blood thundering in her ears.
Cassie takes off, soaring toward the last place she saw him.
She doesn't know where the rest of her team is. They could have been called off to stem some other crisis. They could still be in the city. Cassie doesn't know, and she doesn't stop to ponder. There's only one other person in Bludhaven right now that matters.
She has to find him.
The buildings blur around her. She isn't a speedster. She's never pushed the upper limits of her flight, never tested how fast she can move in the air. She can almost feel wings at her heels, like she's wearing Hermes' sandals once more.
Kon once broke the sound barrier to get to Cissie and Traya when they needed him. Cassie wonders if she's about to do the same.
Three blocks.
It takes an eternity to get there. It takes seconds.
There's a crowd of people and vehicles. Most of them have their backs to the city, as they futilely run. They move sluggishly, like insects caught in amber. They will never make it out in time. Cassie scans the pushing, screaming mass of humanity, ignoring the horror tearing at her heart.
Where is he?
Gray eyed Athena, let me see.
Red and black catches her eye. He's facing the city — going back for someone else — and she doesn't slow down as she angles to intercept him.
Robin. Tim.
She slams into him. Hand on his head to brace his neck, the other curving around his waist.
It's going to hurt. There will be bruises, broken bones. Not even Batman's uniforms are designed to take the full force of a demigoddess moving so fast the world stands still.
She doesn't stop. As soon as he's in her arms, Cassie pulls up, up, away from the people and cars. Away from the wave of destruction hurtling toward them.
Leaving them to their fate.
She can only save one. There's no time to grab anyone else, no room for error or slowing down.
She can only save one, and Cassie made her choice.
Who is she kidding? There was never a choice. She can't lose him too.
The world lights up green behind her, but Cassie keeps her eyes forward. She's not Bart; she can't calculate how fast or far she's gone, she doesn't know the blast radius of what is essentially a nuclear bomb.
A wave of force hits her from behind, sending Cassie and Tim tumbling through the air. She clings to him, attempting to shield his body with her own until she regains her bearings.
She straightens out, readjusting her grip before looking back at the carnage.
Buildings crumble far below. Even this high, this far away, the heat licks at their faces. Anyone at ground zero was probably incinerated on the spot.
They watch silently as Bludhaven is wiped off the map.
She could have. She could have stopped, could have carried more with her. But that would have cost her precious seconds, seconds she didn't have as the bomb went off.
Tim is quiet, and except for the trembling rise and fall of his chest, completely still in her arms.
He's alive.
Kon and Bart and so many others are gone. Dead. But she won't lose another. Not today. It's something she's more than willing to live with.
Some clarification: this story is based on one of the ways I mixed up the timeline before I actually read the comics. In canon both Kon and Bart are alive when Bludhaven is destroyed (though Kon won't be for much longer). The Teen Titans did stop in Bludhaven to help with a crisis, but were called away to deal with some other disaster right before the bomb dropped. The Secret Society of Super-Villains dropped Chemo, a villain described as "a quasi-sentient vat of deadly radioactive chemicals" on the city. Bludhaven was destroyed, Infinite Crisis happened, Kon died, smash cut to One Year Later, where Cassie and Tim were left to pick up the pieces.
In this au, the destruction of Bludhaven happens during OYL, when Bart and Kon are both dead and Tim and Cassie have become super close because everyone they love has been dropping like flies.