The third part of Crisis on Earth-X airs tonight on The Flash and the CW has released a scene for the episode. The majority of heroes are either trapped in the pipeline or on Earth-X while Supergirl (Melissa Benoist) is being bathed in red sunlight to de-power her. This leaves only Iris West (Candice Patton) and Felicity Smoak (Emily Bett Rickards), the two normal, non-costumed people, to try and stop the Nazis and save the day.
In the scene we learn that their trip to Earth-1 was to save the life of Overgirl by capturing Supergirl and transplanting her heart. But Supergirl isn't from Earth-1, she's from Earth-38… did they specifically wait until she was going to be on an Earth that doesn't have Superman? They got the prism to created a red sun generator to weaken Kara enough to cut into her. Felicity and Kara over hear all of this from the air vents where they are hiding. Felicity even makes a John McClane/Die Hard reference. They're going to go find Cisco (Carlos Valdes) and try to wake him up so he can shut of the power and breach them out.
The third and fourth parts of Crisis on Earth-X airs tonight starting at 8 PM on The Flash and then concludes at 9 PM on Legends of Tomorrow… all on the CW.