The Forbidden Territory (Duke de Richleau)

The Duke receives a coded message from his missing friend, Van Ryn, who had been hunting for treasure lost during the Soviet takeover of Russia and is now in prison somewhere in that vast country.

Along with the Duke, good friends Simon Aron and Richard Eaton set off on a secret mission to secure Van Ryn's escape. Without official papers, they lead a thrilling caper, hunted by the Secret Police through Siberia and across the plains, mountains, and forests of Soviet Russia.