A/N: Ok, so I had this really clear idea in my head and it demanded to be written. This takes place in the season 3 finale, when the truth of Sara's murder comes out.

Kill or Be Killed

Thea Queen is dead. She didn't even put up a decent fight, really. The second after the knife slipped between the ribs of the woman dressed all in black, smooth as cutting through butter with her improved upper body strength, her eyes widened and her breath stuttered in shock. It was like she couldn't believe it was happening, couldn't believe she'd actually taken the kill shot. But she had. She had looked in her eyes and driven the knife straight into her heart. As the seconds following ticked by, Thea Queen disappeared from the world in stages. Slowly, and then all at once; a grotesque version of falling in love.

She wouldn't pretend she regretted it for a second as the light died in her opponent's eyes. Thea killed Sara, even if she wasn't aware of it at the time.

"You- you drugged me?!" Thea's head is spinning, unable to comprehend what's happening.

Malcolm's answer is simple, to the point. "Yes."

Thea reels backward, stumbling with the force of the word. "W-Why?"

"She was tracking me. I needed her taken care of. I needed the League off my back."

"I- You made me kill Sara. Sara. I'm your daughter, and you turned me into a killer!"

"I didn't turn you into anything, Thea. Or don't you remember pulling the trigger on me last year?"

Thea's eyes widen in horror. "I'm not a murderer."

A knowing smile stretches across Malcolm's lips and dread settles in Thea's gut. "Oh, but you are. The drug wouldn't have worked if the instinct wasn't already inside of you, waiting to be unleashed."

She may have been manipulated by Malcolm, but she still loosed the arrows that buried themselves in the Canary's stomach and sent her tumbling from the building to land at her sister's feet. The instinct was there, or she wouldn't have done it. At her core, Thea is a killer. To defeat a killer, you have to be willing to be a killer, too.

"What are you gonna do, Laurel?" Ted's eyes are glinting, demanding her to finally voice the endgame she's never put words to before. He's always been good at that, challenging her to identify her purpose when she's flailing.

Her jaw sets and she doesn't waste time thinking about her response. For the first time, she knows exactly what she's going to do. "She murdered my sister. I'm going to kill her."

The ever-expanding pool of blood slows to a stop and she takes a deep, fortifying breath. It's done. There's no turning back. There was no choice to make, really. It was one or the other, kill or be killed, and she won't apologize for choosing herself. She will always choose herself.

They meet on the rooftop, rain pounding down relentlessly. Thea's hair is soaked, but she doesn't care enough to raise the black hood to cover her head. She's too busy staring down at the place Sara fell to Laurel's feet. The video showed her tripping over the edge, arms flailing, but it didn't show the dumpster in her path or the unforgiving pavement below.

"She hit the dumpster on the way down." Laurel's voice is cold with fury.

When Thea whirls around, the other woman's eyes are glinting. She, too, is decked out in black, her blonde wig soaked by the rain.

"Laurel-"

"You shot her full of arrows and left her in the alley with the garbage," she snarls.

"I didn't know-" Thea tries again, desperate. Laurel has to understand.

"That's your great defence? That you didn't know? Ignorance doesn't equal innocence, Thea."

"I wouldn't-"

"You can say you wouldn't have done it all you want, but Malcolm told me how that drug works. You could have resisted if you'd wanted to."

Thea recoils. She's never seen Laurel so consumed by rage before. It's like she's a completely different person.

"What do you want from me?"

Laurel rips the mask and wig off, throwing them to the ground as the rain continues to pound down on them.

"Revenge."

The moment the light left the other woman's eyes, she knew she'd never be the same. She caught her reflection in one of the puddles remaining from the rain and watched, fascinated, as the darkness took over. The life she stole forced its way into her, clouding her eyes. She always thought, if it ever came to that, she'd be utterly repulsed by it. She thought she would fight it. But she didn't. She stood on the rooftop in the aftermath of the storm and she welcomed the darkness, wrapped the cloak of it snugly around her shoulders.

There may only be one body lying on the rooftop, but two women lost themselves to darkness tonight.

The only sounds are their grunts and cries as they circle each other, attacking and defending in turn. It isn't as difficult a fight as Thea imagined when Laurel first lunged. Laurel's style is rough, her technique no match for the League-based training Malcolm has given Thea.

It's kill or be killed, a fight to the death in every sense of the word.

Perhaps it's Thea's over-confidence, or maybe Laurel finding an extra gear, but the women are suddenly face-to-face, weapons pointed directly at each other. A stalemate that only one of them will be able to break.

They lunge simultaneously, but only one of them can connect.

That remaining glimmer of humanity, that one second of doubt, cost one woman a knife through the ribs and the other the remnants of her soul.

At her basest instinct, Thea is a killer. She may not have chosen to kill Sara, but she killed her all the same. While Thea Queen runs from it, spewing apologies, Thea Merlyn accepts it. Thea Merlyn embraces the sense of self-preservation handed down from her father. It is Thea Merlyn who drives the knife home, taking the life of the second Lance sister by choice. And so it is Thea Merlyn who leaves Thea Queen behind with the dead body of Laurel Lance, a Cheshire grin upon her lips as she disappears into the darkness.

A/N: What did you think? I know, not my usual, but I fell in love with the idea of Thea killing Laurel by choice in the finale, since she killed Sara without a choice in the premiere. It will never happen, but I just love the backwards symmetry of it and how it kickstarts Thea's descent into villainy by choice. She embraces her killer instinct because she believes it's the answer to her identity crisis. They've said she's struggling between Thea Queen and Thea Merlyn, so she starts with just Thea and goes from there. The one thing she knows about Thea after finding this out is that she has a killer instinct. Thea Queen has that pure heart Oliver talked about in season 2, she would be disgusted by murder, but Thea Merlyn is her father's daughter and embraces it. Anyways, I've rambled too long about the thought process that went into this. I stuck it in here in part because the fight happened at night, when they could be sleeping, but mostly because I view this as Thea losing her light, so I stuck it in here because it fits under the "and other things" bit.

Reviews would be fantastic!