Lovisa Lundstrom is Peter’s 10-year-old sister who bravely participates in the secret gold-smuggling operation. She is a compassionate character who looks after her younger brother.

Victor Lundstrom is Peter's adventurous uncle and a fisherman who devises the plan to move the gold bullion. His adventurous spirit and leadership play a significant role in the children's involvement in the scheme.

Lars and Mrs. Lundstrom are Peter and Lovisa’s parents, portrayed as loving and protective. They are caught between wanting to safeguard their country and their concerns for their children's safety.

Helga Thomsen is a young girl from Riswyk who participates in the gold-smuggling operation. Known for her courage and tomboyish nature, she often takes the lead among the children.

The Commandant is a German officer in Riswyk, characterized by his violent temper and antagonism toward the townspeople. He poses a significant threat to the children's plan.