Das Geheimschloss

An installment in a series about female detective miss Clever. She investigates a banker who is threatened by a group of criminals, who kidnap his son in an attempt to find a secret codeword. Suspecting an inside agent, she goes undercover in the office and soon finds a trail leading to a sinister gang of criminals. With a lot of cunning and stunts she finds their lair, and then she makes her way back to the police on horseback.