Dreykov captures Natasha and Yelena and brings them to the Red Room where he then uses his chemicals to control them both. However, he has another diabolical plan: to inject gamma-irradiated blood into every Widow, meaning he would control an army of hulks who could hide in plain sight and transform whenever he wanted.
But something goes wrong...
The transformation of the sisters actually breaks the hold of his chemicals and they're free again. Now all hulked up, Natasha and Yelena easily destroy the Red Room and start using the remaining blood to free other Widow's around the world, giving way to hundreds of highly trained assassins with the awesome power of a hulk.