A realistic historical epic that follows a Viking voyage of plunder and destruction, but with a twist.
The Vikings’ true motivations aren’t conquest or plunder, but rather pursuit and destruction of zombie or vampire outbreaks.
Perhaps these outbreaks are the fault of the Vikings in some way, a curse on their people that they failed to contain within their own kingdoms. So now they must sail out in search of outbreaks of the monster plague and annihilate them before they spread — and before the outside world can discover them.
That’s why they wage absolute warfare and total destruction on the isolated communities they attack. They must destroy all traces of the infestations.
Thus, the world sees them as blood-thirsty barbarians, but they are actually saving humanity with every slaughter and every village burned to the ground.
Could tie the story in to the historical attacks of the Vikings for more authenticity. And, as such, could potentially create a franchise that escalates across movies to include other monsters and/or a final showdown with a masterminding evil.