It's a big week for DC fans, as every DC show on The CW is participating in a three-hour crossover event called "Invasion!" Though the end of last night's Supergirl provided a slight introduction to the whole affair, it was tonight's episode of The Flash that really kicked things off. (You can read our review of the episode.)

The entire premise of the crossover hinges on the arrival of an alien species called The Dominators, who are -- you'll be surprised to know -- hostile. Though Earth-38 (a.k.a. Supergirl's world) is plenty used to aliens, the Arrowverse is not quite so used to extraterrestrials. A freaked out Barry Allen, then, assembles his superpowered friends, plus a trusted alien expert, to take on the beings. The arc, which continues tomorrow, lasts through the duration of The Flash, Arrow (its 100th episode!), and Legends of Tomorrow. Before we move away from The Flash, though, The CW is offering an inside look at the process behind filming the latest episode.

In a behind-the-scenes video entitled "Inside the Flash: Invasion!," the network (via Todd Helbing) offers a brief look at the episode overall. Helbing explains how Barry comes to find out about The Dominators, and what his next steps are afterwards. Check it out, above.

If you haven't watched tonight's episode of The Flash yet, this video is a great intro to the arc overall. If you have, it's still a fun look at some of its highlights. In the video, we get glimpses at characters from nearly all other CW DC shows, save for Legends of Tomorrow. Oliver Queen, Felicity, and Thea Queen pop in from Arrow, while Supergirl herself shows up at the end of the video. In true Danvers fashion, Kara is more than eager to help, though Felicity voices some key doubts.

As far as promotional videos go, this is a cute shoutout to fans, but it doesn't explain the episode in a particularly deep way. Most of us already knew the premise of "Invasion!", and while it's cool to hear some of Barry's rationale from one of the show's executive producers, this clip doesn't have a ton to offer otherwise. Still, it's a lighthearted little extra to check out before more like it pop up in the Extras section of The Flash's season 3 DVD.

All in all, you can add this to the ever-growing list of "Invasion!" promotional material, and what is likely a small piece in a larger upcoming behind-the-scenes look at the crossover special. This will be a nice little treat for diehard fans of The Flash, even if it's not the most compelling overall.

Invasion! continues tomorrow night @8pm on the CW with Arrow, followed by Legends of Tomorrow on Thursday, December 1st @8pm. The Flash returns next Tuesday @8pm with ‘The Present’.

Source: The CW [via YouTube]