Death Trap — Charles Whiting

Common Smith is in a race against time to retrieve sensitive British intelligence before it falls into enemy hands
Yugoslavia, Winter 1924. The British official courier plane from Cairo to Gibraltar has been forced down in the mountains off the Yugoslavian coast by snow. 

The plane was on its way to London bearing vital documents about Moscow's plans for the Balkans, including an uprising in Yugoslavia. It is vital that no one finds these plans, including the Royal Yugoslavian Secret Police, for they too have communist sympathisers in their ranks.

Now, in a race against time, Common Smith and the crew of the Swordfish must sail to the island of Vis, then up the River Dvar and smuggle themselves into the snow-bound mountains. Their mission: recover the British airmen and the sensitive documents they were carrying.

But the elements and Yugoslavian Secret Police are not the only forces Common Smith is contending with. A mysterious Communist leader is hiding out in these mountains with his men, and they know about the crash too...

A gripping, edge-of-your-seat race against time from one of the masters of military adventure fiction.