Overland: Romantic Adventure by Mark Stephen Levy

After Danny Benson finishes medical school he wants nothing more than to start his residency and settle down to marry his fiancée, Heather. But on the day of his final exam, Danny receives a letter. The engagement is off. Heather's baffling explanation: she's going to London where she will travel overland on the Magic Bus to Kathmandu. His plans shattered, Danny finds himself on a journey thousands of miles from home, in search of the woman he loves. When he discovers her on a bus somewhere east of Europe the reunion is less than stellar. They spend the entire ride to Afghanistan debating whether to stay together or break up forever. Now, arriving in Kabul, exhausted from their long bus trip, fate will decide their dispute for them. The following day, December 27th, 1979, the Soviet Union invades Afghanistan. What happens next is their moment of truth as Danny and Heather collide with history.