On the eve of D-Day, a paratrooper squad is sent to destroy a German radio tower in an old church; however, their plane is shot down before they can reach their target, leaving only five apparent survivors, Corporal Ford and soldiers Boyce, Tibbet, Chase and Dawson. Dawson is killed by a landmine but the team continues onward, running into a French woman named Chloe who agrees to take them into the village where the radio tower is located. The soldiers learn that Chloe lives with her 8-year-old brother Paul and her aunt, who has been disfigured by Nazi experiments taking place in the church. After Tibbet and Chase depart to check the scheduled rendezvous site, the remaining soldiers are forced to hide in the attic when a Nazi patrol performs a routine inspection. But when SS Hauptsturmführer Wafner attempts to rape Chloe, Boyce attacks him, forcing the soldiers to take him prisoner.
Attempting to reach the rendezvous point, Boyce witnesses the Nazis burning disfigured village residents. He is nearly caught by a dog and is forced to take refuge in a truck carrying the bodies of some of the other paratroopers. Once inside the base, Boyce learns that there are various experiments taking place in the lab, based around a mysterious liquid compound the Nazis discovered, by distilling an ancient tar through human bodies, from under the church. Boyce takes a sample of the serum and rescues Rosenfeld, another member of the paratrooper squad who was captured by the Nazis, and escapes the castle.
Back at the attic, Wafner refuses to explain what the serum is when questioned and is subsequently beaten by Ford. As the squad prepare to assault the church, Wafner attempts to escape, shooting and killing Chase in the process, driving Boyce to use the serum on Chase after his death. The serum restores Chase to life, but he immedi- ately begins to mutate, showing inhuman strength, a resistance to gunfire, and turns hostile, forcing Boyce to pulverize Chase’s head to stop him. In the midst of the chaos, Wafner escapes while taking Paul as a hostage, although part of his face is blown off by Ford in the subsequent shootout.
With time running out until the deadline when the radio tower must be destroyed, Boyce convinces Ford that destroying the laboratory has to be their priority. While Rosenfeld and Tibbet create a distraction at the main entrance, Ford, Boyce and Chloe enter the base through the sewers Boyce previously used to escape, with Boyce and Ford planting the explosives while Chloe rescues Paul. Ford is attacked by a mutated Wafner, who has injected himself with a combination of untested serums, which heals his injuries while driving him increasingly insane. When Boyce manages to distract Wafner, the injured Ford injects himself with another sample of the serum, allowing him to force Wafner down the pit where the compound was discovered, but he then forces Boyce to leave him behind and finish setting off the dynamite. Boyce succeeds in blowing up the radio tower and the laboratory, escaping just in time for the church and radio tower to collapse behind him.
After the destruction of the radio tower, Boyce reports to their superiors that Ford chose to plant the bombs inside the church rather than outside to ensure its destruction, choosing to avoid mentioning the serum or the lab as Ford believed that neither side should possess the serum. The military accepts this story and the soldiers are informed that they will be reassigned to another company as the war continues.