SPOILER WARNING: The following article contains major spoilers for Overlord, in theaters now.
As much as J.J. Abrams' Bad Robot Productions loves "mystery box" movies, Overlord is pretty straightforward. Set during World War II, it's a non-intricate period piece on D-Day that focuses on the Allies, specifically an American troop of paratroopers, who are shot down behind enemy lines. They then to take down a church tower that's jamming radio signals on the French coast, thus giving the German oppressors the upper-hand.
When the squad eventually manages to infiltrate the compound, they find more than just Nazi soldiers waiting. The establishment turns out to be a lab for gruesome experiments to produce zombies for the frontlines, a "thousand-year army" as the Germans call them. However, thanks to their sharp military tactics and a few strokes of luck, the Americans blow the church up, destroy the tower and win this particular battle. But the war's far from over and in its finale, Overlord sets up a couple of intriguing angles for a sequel.
More Secret Nazi Labs
Overlord's zombies have been created thanks to the Germans burrowing deep into the Earth below the church, uncovering unique elements in the soil that can reanimate life. They use this to create a special serum to revive the dead as mindless soldiers.
However, as the villainous leader Dr. Wafner (Pilou Asbaek) suggests, other labs may exist, not just in France, but all across Europe. Seeing that they know what type of soil to look for, it's easy for the Nazis to scour and test various locations, constructing other labs once they find the best places to mine.
Even if this church was the only location with this unique soil, there's no reason the serum derived couldn't be transported to other sites for replication. After all, the Axis would want squadrons of zombie soldiers at various camps, and from a tactical standpoint, it's smart not to keep your trump card (aka, all the serum) stocked in one location.
A sequel could easily follow the Allies marching on other labs, destroying the serum once and for all, to ensure their enemies can't complete the mission of building an immortal army.
The Hunt for the Surviving Mutants
When the dead are injected with the serum, they don't just turn into zombies, they become grotesque mutations. These abominations are of different sizes, speeds, strengths, appetites and they even look different.
Despite the church collapsing in the finale, it's not far-fetched to think these kinds of monsters survived. The holding cells were deep below the church, after all, reinforced to keep the prisoners secure, so there's a possibility the blast didn't fully destroy the base and that the strong did escape.
Overlord ended with the Americans basing camp right outside the church, so a follow-up can deal with the remaining mutants/zombies attacking them and the subsequent retaliation. Overlord also set up a separate hunt earlier on, when it showed the dead remains of a mutant jackal, apparently infected by the land itself.
One of these jackals later attacked the Allies, but after they escaped, the issue was surprisingly never addressed again. Therefore, the opportunity is there to deal with these jackals, or other mutated animals, as they stalk the soldiers; that would certainly create an intriguing predator-prey dynamic in the dilapidated town and adjacent forest.
Directed by Julius Avery from a script by Billy Ray and Mark L. Smith, Overlord, starring Jovan Adepo, John Magno, Wyatt Russell, Bokeem Woodbine, Pilou Asbaek, Jacob Anderson and Iain De Caestecker, is in theaters now.