Timeline: shortly after _Civil War_.
Black Widow is on the run when her attempt to hide out is broken by the delivery of an unexpected package.
Now she has to get back together with her family (of Soviet spies) to take down the Red Room, responsible for her creation.
It's basically a Bond flick, but set in the MCU.
Most superhuman feats are either action movie cool with no explanation, or justified by the top tier spy training/brainwashing of the Red Room.