Metal Gear Solid 4: Guns of the Patriots — stealth action game with first and third person views. Snake infiltrates the area where Liquid's army is based and is ordered to meet with a nearby US Army detachment. Dr. Emmerich provides support to Snake over the radio, and is assisted on the spot by a small robot, Metal Gear Mk 2. On the way to the meeting point, Snake meets Drebin 893, a black marketeer who injects Snake with nanomachines, allowing him to use the latest generation of weapons.
Having reached the meeting place, Snake encounters a patrol squad, led by his old friend Meryl Silverburg, and learns of Liquid's location. Snake moves on, but as soon as he finally manages to get to Liquid, he activates a signal that immobilizes Snake, the patrolmen and other soldiers equipped with nanomachines. After the fall, Snake sees Dr. Naomi Hunter, who once injected him with the FOXDIE virus.
In a coded message, Naomi reveals that she was forced to do research for Liquid and asks Snake for help. Snake travels to South America and encounters Vamp and an unknown cyborg. He then listens to Drebin's message about the Patriots, networked artificial intelligence products that control nanomachines.
Snake finds Naomi, who says that Liquid plans to use Big Boss's biometric data as a key to the Patriot system core and take control of the Sons of Patriots' weapons system. After conducting a test, she concludes that Snake's rapid aging is due to genes, and the FOXDIE virus will kill him within 6 months. Snake uses a deadly new sample of the FOXDIE virus, turning him into a walking biological weapon. With the help of Drebin and Raiden (who has become a cyborg ninja), Snake and Naomi manage to leave the country.