Sam and Natasha immediately jumped up at the sight of the Winter Soldier, ready to fight. Steve's jaw dropped open at the sight of the Doctor and River - when Bucky came out of the TARDIS, the inhaler fell from his hand (though he still held onto the fob watch carefully). "You're alive," he said, stunned. "You're... Bucky. Bucky!" He threw himself forward, at his friend.
Bucky caught him, holding tight. The Doctor had shown him their history, letting him see all the moments that had made up James Buchanan Barnes, breaking through Hydra's foul work. The form he was holding was bigger, taller, but the wheezing breaths, the trembling muscles, were all too familiar. Bucky Barnes glared at the rest of the Avengers. "What the hell happened to him?"
Natasha recovered first. "Poisoned. Countering the serum. We don't know how to fix it yet."
Steve, meanwhile, was hanging onto Bucky, looking back and forth between River and the Doctor. "You're alive. I thought... he said..."
River smirked. "I'm still the man who killed the Doctor," he said. "As far as the universe knows."
Steve was still in shock, but he nodded, and leaned against Bucky as he turned back to Tony. "What do you want me to ask it?"