The sinister lord Miraz (portrayed by Sergio Castellitto) has not only betrayed and murdered his own brother but has also kept Prince Caspian (played by Ben Barnes) under tight control in a bid to seize the throne for himself. When Miraz's treachery reaches a breaking point, Caspian is forced to flee the castle in the dead of night, seeking refuge in Narnia's untamed wilderness. As he escapes, fear drives him to blow a magical horn as a desperate call for help.

Meanwhile, in another world, Peter (William Moseley), Susan (Anna Popplewell), Edmund (Skandar Keynes), and Lucy (Georgie Henley) are living the lives of ordinary students on the streets of London. But the sound of the horn rekindles their connection to Narnia, summoning them back after 1,300 years have passed in that realm. Narnia, now subjugated under the rule of the Telmarines, desperately hopes for the return of its once-great kings and queens to restore freedom and peace to the land.