When an army drum is breached and a mysterious chemical gas is released into a nearby cemetery, the dead return to life with only one thing on their minds brains! The zombie menace quickly descends upon a group of misfits who must fight for survival as they are picked off one at a time by a horde of the undead.

Horizon takes seven people who are some of the highest flyers in their field - a musical prodigy, a quantum physicist, an artist, a dramatist, an RAF fighter pilot, a chess grandmaster and a Wall Street trader. Each is put through a series of tests to discover who is the most intelligent?