Endgame starts in a world following "the snap" delivered by Thanos that extinguished half of all life within the galaxy in an instant, without a trace, in his effort to bring what he feels is a much-needed balance and tranquility caused by overcrowding interests.  After a brief intro, we fast forward five years to find a world that has had trouble moving on from the loss of their many loved ones, especially the surviving Avengers (conveniently, all the characters that comprised of the first core team are among them), who feel a particular sense of guilt for not being able to save the billions they were sworn to protect.  However, a new idea develops to find a way to reverse the situation through a risky and highly improbable gambit in which they must try to traverse time and space to re-connect all of the Infinity Stones and bring back all of those who vanished without losing the good things that have happened since that fateful day. Robert Downey Jr., Chris Evans, Chris Hemsworth, Mark Ruffalo, Scarlett Johansson, and Jeremy Renner, and many, many, many, MANY more appear in this massive crossover event.