There will likely be no plot details for Avengers 4 released until after Avengers: Infinity War hits theaters on April 27 either, and even if there is an official synopsis reveal, it likely won't be too extensive.
Iron Man, Thor, the Hulk and the rest of the Avengers unite to battle their most powerful enemy yet -- the evil Thanos. On a mission to collect all six Infinity Stones
The bad news is, there are about ten movies going on in "Captain America: Civil War," which is at least seven too many. The good news is, most of them are fun, and there are enough rousing moments to elevate the movie to Marvel's top tier.
Captain America: The Winter Soldier" is a very good movie, the rare film in this genre that serves as both entry point and continuation. For a change, you can walk in cold and you won't be too lost.