Odyssey.Wad is a compilation of 5 levels of the Ancient Series over the course of a month as individual episodes Each level is set in a different time period or locale. The concept being that the UAC agent (you) are travelling thru time to stop the influx of those friendly neighborhood beasties. The beasties have gotten their claws on some kind of time travel device.....You must go back to the 5 different time zones and eliminate the threat to history otherwise the distortion ripples would be so terrible, that life as we know it today would cease to exist.