The Flash, Arrow, Supergirl, DC's Legends of Tomorrow Crossover Starts Nov 28

Darn, Entertainment Weekly, give us some high res photos to make into backgrounds.
We're so hyped four the four-day cross-over of The Flash, Arrow, Supergirl, DC's Legends of Tomorrow. How it all connects to invading aliens, The Dominators, well, we would like to know.
It all starts on Nov 28.