Michael Strogoff, by Jules Verne. Part V.

This is the account of the perilous mission of Michael Strogoff, courier for Czar Alexander II, who is sent from Moscow to the besieged city of Irkutsk, where the governor, brother of the Czar, has taken his last stand against a Tartar rebellion led by the fearsome Feofar-Khan. 

When telegraph lines are cut between the Russian Far East and the mainland, Strogoff must make his way through hostile territory to warn the governor of the return of the traitor Ivan Ogareff, a disgraced former officer who seeks vengeance against the Tsar’s family by the destruction of Irkutsk. (Adapted from Wikipedia.)