Leader extracts all of Bruce's Gamma power, stores it in batteries and then starts unleashing it on human test subjects, trying to build his own army.
Bruce is recovering in Betty's quarters in Leader's base, but once he learns of Leader's actions, he shoots himself in the leg in an attempt to bring the Hulk back out. It doesn't work.
Bruce and Betty then charge into Leader's lab, guns blazing. Baracading themselves in, Betty gets behind some gamma ray shielding and Bruce shoots the Gamma containment cell. Gamma radiation is released and Bruce becomes the Hulk once again.
Hulk fights his way though Leader's robots, takes on the test subjects and then finally confronts Leader. He takes the batteries the Leader had created to store the Gamma power and eats them.
After finally defeating Leader, Betty escapes by boat and Hulk escapes into the wild.