Metal Slug 4

One year after the events of Metal Slug 3 and 6 , the world is under the threat of a mysterious and deadly cyber virus that threatens to attack and destroy any nation's military computer system. With Tarma Roving and Eri Kasamoto unable to help out due to their own assignments in the matter, Marco Rossi and Fiolina Germi are called in to investigate the situation and are joined by two newcomers, Nadia Cassel and Trevor Spacey. In their investigation, the group discovers that a rich terrorist organization known as the Amadeus Syndicate is behind the plot and has allied with General Morden's Rebel Army. They head into battle against Amadeus' forces, hoping to destroy the cyber virus before it gets the chance to wipe out the entire world's military computer system.

Halfway through the game's story mode, the player is confronted by who they presume to be General Morden. In the final stage, they find an underground facility where android doubles of Morden are being manufactured. Allen O' Neil fights the player and is also revealed to be a machine replica. The player confronts the leader of the syndicate, a man tentatively called "Doctor", who attacks with a series of powerful robots, but he is defeated and is trapped in his own devices as the base self-destructs, killing him.

If the player safely escapes the base's bonus explosion stage, the credits will show the main cast eating a feast of food, but if the player gets caught in the explosion, the player character will appear in the hospital, bandaged and bed-ridden, being brought get-well gifts of food from both Tarma and Eri. After the credits, a single computer monitor is seen transmitting data to an unknown location before shutting down.