“Mercy Mission” is the fifth episode of the Star Wars: The Clone Wars television series’ fourth season. It is the first in a two-part story storyline about R2-D2‘s and C-3PO‘s adventures. It aired on October 7, 2011.
“After groundquakes have devastated the planet Aleen, a Republic relief effort arrives, including the droids R2-D2 and C-3PO. When the native Aleena‘s pleas go unheard, it becomes the duty of the droids to embark on a surreal journey through Aleen’s subterranean world to save the planet.”