In 1976, four friends - Dan, Fred, Tim and Thierry - are on a bus along the hippie trail from London to Kathmandu. But everything is not going according to plan.

After a drug deal goes wrong, the boys barely escape with their lives. Thousands of kilometers, numerous acid trips, accidents, nightclubs and a pair of beautiful Siamese twins later, they finally reach the counter-culture capital of the world, Kathmandu, and Fred disappears with the drug money.

A quarter-century later, mysterious emails invite the other three to pick up their share of the money, and they decide to reunite in Kathmandu. Soon, a trail of kidnapping and murder leads them across the Roof of the World.

With the help of Dan's backpacking son, a tattooed lady and a Buddhist angel, the ageing hippies try to solve a 25-year old mystery that takes them amongst Himalayan peaks, and towards the inevitable showdown with their past.