We're Assassins, Not Avengers

Three

The gala was held inside of a ballroom. The girls weren't surprised to see Tony Stark, Steve Rogers, Natasha Romanoff, and Wanda Maximoff among the guests. All of them were dressed up and glancing around the room suspiciously.
The girls figured they were the only Avengers here but that changed when they turned to see Sam Wilson and Bucky Barnes standing along the wall.
"Split up," Nightshade said with a smile.
As she walked to table of refreshments, she was approached by the Winter Soldier, "Care to dance?"
She nodded. He took her hand and lead her to the dance floor. Nightshade figured he suspected her until she realized he was still looking around the room. He was just using her to blend in, she realized.
"You're Mr. Barnes, right?" He nodded. "Are you guys really going to catch the three assassins?"
He smiled down, "Hopefully."
"What do you plan to do to them?"
He shrugged, "Most people want them put away, but I think we'll try to get them on the right track. You know, considering both Nat and I were assassins too."
She looked up, "And if they don't want to?"
He shook his head, "Of course they'll want to."
"Whoever these guys are, we'll catch them. Don't worry."
She bit her lip, debating with herself only to give in, "Are you sure they're guys?"
The song ended so Nightshade parted ways and left for Jordan.
They danced before he offered her a drink. She repeated her routine, poisoning her own glass and swapping it with his. It went smoothly. This time, she stayed close by until he dropped dead. As his body hit the ground, Tony Stark rushed over and searched the surrounding faces for suspects. Nightshade observed, making note he barely glanced over the women in the crowd.
Across the room, Viper and her victim were unaware of the commotion on the other side. For tonight's kill, she needed a cleaner job, so, she adopted part of her partners methods. She pulled out a syringe, filled with viper venom, and inserted it into Mr. Santiago's neck as they danced. She pushed the liquid out before he could stop her. As he stepped back and brought his hand to his neck, she slipped the syringe into her sleeve.
He pointed a finger at her, "You! What did you do-" She drew back her fist before he could cause too much of a scene. He was knocked out and on the ground before he got another word out.
The crowd around them stepped back, well, most of the crowd.
Steve Rogers stepped forward, "What's going on here?"
Viper put on a show, "We were dancing and he started making me uncomfortable so I stepped back to leave and he was coming after me! I didn't know what else to do!" She had tears, fake of course, building up in her eyes at this point.
Captain America put a comforting hand on her shoulder, "It's okay, I'll take care of him."
Viper nodded and wiped her eyes, "Thank you. I just want to go home." She wrapped her arms around herself and walked around him, towards the exit.
Upstairs, Ghost has gotten the third and youngest Santiago heir alone and was going in for the kill when they heard a commotion downstairs.
"Grab her! He's dead!" Yelled a voice. Tyler turned to see what was going on but Ghost stopped him, deciding to go for the damsel in distress part, "Please don't leave! I'm scared."
Tyler was quick to build his ego, "I've got you." He assured, pulling her into his arms. As his arms wrapped around her, she plunged a needle into his vein and stepped back.
As his body hit the ground, she closed the door behind her.
At this point, her necklace was giving off a slight buzz and she knew one of the others needed to leave.
She slipped through the doors and out to the street to see most of the Avengers taking off in different directions.
Ghost saw the car parked alongside the others and jumped in.