In 1638, when a large piece of validium fell to Earth, Lady Peinforte found it and sculpted it into an image of herself holding a bow and arrow, calling it "Nemesis." The Seventh Doctor found the statue, removed the bow and arrow, and placed it onto the rocket-sled, firing it off into space. De Flores discovered information on the Nemesis and planned to use its destructive power to bring the Fourth Reich into existence. He also had the bow required to reactivate it.
Once his second-in-command, Karl, delivered information on where and when the Nemesis would crash back into the Earth, he wasted no time in going to retrieve it.
Once arriving at the crash site with a squad of his soldiers, de Flores decided to let the police, who had cordoned off the area, guard the Nemesis until it cooled down from the impact from space and retrieve it. When de Flores and his men decided to retrieve the Nemesis, he found that all the police officers had been killed by a form of gas but paid little attention to this. They instead headed straight to the Nemesis and attempted to extract it from the meteorite in which it was encased.
De Flores noticed that the arrow required to reactivate the Nemesis was not there and when the Seventh Doctor and Ace arrived, he demanded they hand the arrow over. The Doctor calmly told de Flores that not only did he not possess the arrow, he also warned him that the police around them were killed by highly advanced extraterrestrials.
When de Flores learned that they did not have the arrow, he was prepared to have them shot. However, he was distracted by a spaceship landing, which was revealed to contain Cybermen who had the intention of taking the Nemesis for their own purposes.
De Flores' men engaged in a pitched battle with the Cybermen but were quickly decimated in the one-sided fight. The time-displaced Lady Peinforte, who was also searching for the Nemesis, arrived during the fight and killed a couple of Cybermen with golden arrows. This gave de Flores and Karl enough time to escape the conflict, to regroup and fetch some gold dust.
After seeing a Cyberman ship being blown up, de Flores went to investigate and found that the Cybermen had hidden the Nemesis in Lady Peinforte's tomb. By this time, however, Lady Peinforte had barricaded herself in and was holding back the Cybermen with gold arrows. De Flores informed the Cybermen that because he and Karl did not share the Cybermen's vulnerability to gold they were willing to fetch the Nemesis for them in exchange for half of the planet; de Flores intended to betray the Cybermen instead.
De Flores confronted Lady Peinforte in the tomb with her servant Richard Maynarde. Richard threw the arrow needed for its activation at the Nemesis, hoping to create a distraction to let Peinforte and him escape. De Flores let them both go and the Cybermen entered the tomb soon after. He was prepared to use the Nemesis to destroy them but found that he was missing his bow and therefore could not activate the Nemesis. De Flores threw his gold dust at the Cybermen, but Karl restrained him and declared that his intention was to betray de Flores to the Cybermen.
Karl overpowered the Cybermen later and allowed de Flores to escape from his captivity; He had been loyal to de Flores all along. De Flores and Karl discovered the Doctor's location and found him in possession of the bow, arrow and Nemesis itself. De Flores attempted to take them all from the Doctor, but the Cyber-Leader arrived and gunned both de Flores and Karl down. (TV: Silver Nemesis)
Alternative timeline Edit
In an alternative timeline accidentally created by the Seventh Doctor and Ace in October 1944 in which Nazi Germany won the Second World War, de Flores remained a senior Nazi officer until well into the 1960s. Elizabeth Klein claimed that he had "always the Führer's favourite." When the proper timeline was restored and Klein was left stranded in 1944, she escaped to South America and joined de Flores in self-imposed exile. Klein told the Doctor that she hoped that de Flores would succeed Hitler as Führer when the Fourth Reich was established. (AUDIO: A Thousand Tiny Wings)