How do you ease yourself back into documentary film-making when your last commission ended in three months' terrifying captivity as a hostage of the Taliban?

Following his eventual release in 2008, award-winning Sean Langan — best known for his one-man-and-his-camera reports from the world's troublespots — took a sabbatical to recover. He returned to our screens on a much gentler assignment in East Africa.

Sean was on a mission to ride the Tazara railway from Tanzania to Zambia. And he made a most affable host as the heaving train set off from the port of Dar es Salaam to the Zambian copper belt and back again.

Elephants wandered across the tracks and excited children ran alongside. Traders even planted themselves at scheduled and unscheduled stops.

But Sean was not content simply to take a jolly journey. He wanted to find out why the once thriving passenger and goods railway is in crisis.

Dubbed Africa's 'Freedom Railway' it was built by the Chinese after Tanzanian independence as an "investment" in Africa, carrying the region's hopes of prosperity.

Now there are daily derailments, trains run out of fuel and mechanical breakdowns. Sean wasted no time getting to know his fellow travellers, including the carriage stewards, controllers and maintenance crews who battle to keep the train going against the odds.

At one point, when it shuddered to a halt and remained stranded behind an accident, Sean visited the driver's cab for a chat and discovered the speedometer was broken — so they have to guess how fast they are going.

Eventually the train limped back to Dar es Salaam, and Sean headed for Tazara HQ to track down the elusive Chinese railway advisers to find out what has gone so wrong.

He didn't find any satisfactory answers, but had climbed back on the film-making horse successfully.