Leon returns as the protagonist of Resident Evil 4. He is a special agent for the US government, and is assigned to rescue the newly-elected President's daughter, Ashley Graham, who is being held somewhere in Spain. Her kidnappers turn out to be part of a cult known as Los Illuminados, which has taken control of the local villagers with parasites known as Las Plagas. Leon teams up once again with Ada Wong, and Luis Sera, a former researcher for Osmund Saddler, leader of the cult.
Source from Wikipeida