Agents Sydney Bristow and Marcus Dixon are hot on the trail of a drug lord who has created a mind-control drug so potent that in the wrong hands it could be one of the world's most dangerous bioweapons. Determined to halt production of the substance, the agents go undercover as dealers. Their approach proves to be successful when the drug lord invites them to his estate -- the perfect chance for Sydney to snoop around and find the location of the main lab.

But things don't go quite as planned. A government agency interferes with APO's mission; Sydney is forced to ingest a dose of the drug and commanded to turn on her APO counterparts; Dixon is taken hostage; and someone believed to be an ally turns out to be more foe than friend....