During World War II, the Oversteegen family hid a Jewish couple in their home.[3] Freddie Oversteegen and her older sister Truus began handing out anti-Nazi pamphlets, which attracted the notice of HaarlemCouncil of Resistance commander Frans van der Wiel. With their mother's permission, the girls joined the Council of Resistance, which brought them into a coordinated effort.[2]Freddie was fourteen years old at the time.[3][4]

Oversteegen, her sister, and friend Hannie Schaft worked to sabotage the Nazi military presence in the Netherlands.[5] They used dynamite to disable bridges and railroad tracks.[6] They also smuggled Jewish children out of the country or helped them escape concentration camps.[2]

The Oversteegens and Schaft also killed German soldiers, with Freddie being the first of the girls to kill a soldier by shooting him while riding her bicycle.[1][5] They also lured soldiers to the woods under the pretense of a romantic overture and then killed them.[1][5]Oversteegen would approach the soldiers in taverns and bars and ask them to "go for a stroll" in the forest.[2][5]