Complex sentence: The package is revealed to be a case of Super Soldier Serum, enough to form an army, but Hawkeye's clients expose themselves as undercover S.H.I.E.L.D agents.
Split into simpler sentences: The package is revealed to be a case of Super Soldier Serum enough to form an army. But Hawkeye's clients expose themselves as undercover S.H.I.E.L.D agents.