Last night, the CW’s Supergirl and Arrow combined for the first night of a four-hour, four-series two-parter, concluding tonight with The Flash and, at 9 p.m. ET, DC’s Legends of Tomorrow. The extended story line involves a parallel world, Earth-X, in which the Nazis won WWII (and yes, they dropped a requisite Man in the High Castle joke), with the familiar heroes from the CW superhero shows facing off against their evil, darker-dressed counterparts from this other world. As last night’s part of the adventure ended, the good guys had been captured, and held prisoner in an Earth-X facility, while their lookalike bad guys were free to roam, and terrorize, “our” Earth.