In the events of Zombie Dawn, the Overlord (you) managed to zombify and take over most of the world. The problem now is that there aren't many humans left to munch on, so the zombies have started to fight among themselves over this increasingly rare resource.
In Zombie Dawn Multiplayer: Fight of the Living Dead, it's up to you to lead your horde of undead against other overlords in a real-time strategic race to capture and/or zombify as many of the remaining humans as possible. Doing so will earn you Research Points, with which you'll discover some awesome new power-ups, traits and modifiers. Using these, you'll be able to mould your rotting mob to fit your style of play, and better fend off those lesser overlords.