Underground - Avengers: Assemble (S2:E1)

Basic Info
"Underground" is the first episode of the second season of Avengers: Assemble. It is the first episode following the finale of the first season, which took a period of two whole years to finish airing.

Synopsis
Ant-Man investigates a problem with the atomic structure of the Earth while Steve, Natasha, and Clint try to figure out how to help Hulk return to Bruce Banner. Thinking it's a false alarm, Tony is hesitant to help out Ant-Man when he discovers a menace lurking beneath the ground and is taken hostage while trying to figure out what--or who it is.

Trivia

 * This episode was released just four months after the re-release of the Season 1 finale. This is due to the major rise in popularity the series received upon its re-release.