March 1944, Germany is losing the war. Nazi scientists are constructing a deadly weapon in a secret laboratory under the guidance of the SS. Ahron Roth, commander of U-931 fears for the fate of Germany, the devastation that will come with the upcoming allied invasion. Ordered back early from patrol to Saint-Nazaire, France he discovers his secret love Ginette, a young French girl has been spirited away by her father. Taken to the Reichstag in Berlin, Roth, born in Germany, raised in America and speaks English is ordered on a special mission, one that will change the war back in Germany's favour. The plan is to take two SS officers, Fuchs and Vogel, in U-931, together with a ‘dirty (black) bomb’ and deploy it in Washington D.C. The ‘dirty bomb’ is part of a deception as it will be simultaneously detonated alongside three V1 rockets, launched on the capital from modified type XX1 U-boats, located off the eastern seaboard. The Nazi’s believe they can dupe America into believing Germany can launch a nuclear strike on the U.S and this will stop the invasion or change the terms of surrender. Himmler is overseeing the operation, but is distancing himself. He is considering other types of attack on America, believing that Germany can launch their own ‘Pearl Harbour.’ A reconnaissance plane spots U-931 at Peenemunde rocket facility on the Baltic coast where the ‘dirty bomb’ is to be loaded. Rear Admiral Sullivan, R.N, organises an air attack on the sub, which is unsuccessful. U-931 disappears and its whereabouts are unknown. H.M.S Zenobia, a flower class corvette, commanded by captain David Prince is proceeding to Portsmouth, preparing to take part in the upcoming invasion. U-931 and H.M.S Zenobia approach the English Channel at the same time, unaware of each other. Zenobia attacks U-931 but is outwitted by Roth and is sunk. SS major Fuchs orders the sub to the surface as the ship sinks. A lifeboat, carrying survivors including captain Prince drifts towards the sub. Fuchs and Vogel open fire in a murderous attack. Prince isn’t killed straight away and returns fire, killing Vogel. The sub disappears again, but Fuchs orders Roth that because of his upbringing in the U.S, he will take the place of Vogel. MI6 intercepts a one word coded message from U-931, ‘Surtr,’ which describes a German God and a black armageddon. Sullivan hunts the missing Roth for the murder of Zenobia's crew. O.S.S contacts Sullivan and explains possible links to a potential sub-launched rocket attack on the invasion forces and U-931’s possible connection. Meanwhile another U-boat with the number U-931, limps into La Rochelle, France as part of a German deception. The real U-931, now disguised as a U.S submarine, approaches a secluded inlet on the American coast. U-931 cannot be found, so the OSS dismisses it as a threat. In Carolina, Roth, Fuchs and the ‘dirty bomb’ are unloaded. Two small boys see the sub; Roth stops Fuchs from killing them. Roth tells Schmitt, the boat's chief, to search the sub, as he believes Fuchs has planted a bomb on board. He tells Schmitt to sail to Argentina, not France, as he fears for the lives of the crew if they return home. Roth and Fuchs travel to Washington in a truck with the bomb hidden amongst crates of ‘Camel’ cigarettes. Both men have conflicting views over the morals of the mission and argue. Stopping to refuel on a deserted road, their truck breaks down but a young man stops to help, Fuchs kills the lad, justifying the murder as they need his truck. The codeword ‘Surtr’ is sent to the three awaiting subs to launch the V1’s at 0700. The moment to detonate the ‘dirty bomb’ arrives, but Roth's conscience wins and as he tries to stop Fuchs, a fight ensues; Fuchs is killed. The V1’s are launched, but one blows up killing all on board. The other two reach Washington and explode. Roth drives away from the city. He disposes of the bomb and heads south, with ideals of getting back to home and Ginette, still unsure if he’s done the right thing for his country. A day before the Washington attack a biological weapon (the one that was described in the prologue) is activated by two more SS officers at Grand Central station, New York. This weapon releases a slow acting plague or ‘black death’ pathogen which infects hundreds of unaware train passengers in the station.The two men escape to Florida, unaware that they are also contaminated, as the device was designed to release the agent onto them also, infecting more people as they travel south. They are to rendezvous with a sub, U-931; to take them back home, something Himmler has made sure couldn’t happen, he had planned that the two SS officers would spread the disease down south through America, part of his master plan to bring America down. This would be the Nazi’s Pearl Harbour.