This year, the CW's annual crossover event between their superhero shows has doubled in size. "Arrow" and "The Flash" are now joined by "Legends of Tomorrow" and "Supergirl" (which has made a network jump from CBS to the CW). This double-sized crossover will run one week in November, from Monday to Thursday night, with all four shows coming together to tell one massive story.

A new Twitter picture from "Arrow" lead Stephen Amell teases that crossover. The picture from the series' Vancouver sets shows five CW heroes -- Arrow, Atom, Flash, White Canary and Supergirl -- from the waist down and lounging.

While the plot for the crossover has yet to be revealed, executive producer Marc Guggenheim has said that Supergirl will be the event's unifying thread. "It's an external threat from outside the shows that will involve Supergirl coming over to 'The Flash,' then 'Arrow' then 'Legends of Tomorrow.'"

The CW's superhero lineup kicks off another season when "The Flash" returns on Tuesday, October 4. The four-part crossover will air later this fall.