Jack is lying in a freezing tent, deep in the mountains 300 miles into the Arctic circle in Northern Finland, too ill to move. Outside, the merciless wind is dropping the temperature to minus 28. The nearest major hospital is 250 miles away, and he's 50 miles across savage, storm exposed terrain from the nearest road. If ever there is a moment so far in Jack’s adventures on Adrenaline Junkie when they look like they could come to an end, then this is it.

Jack sends the recruits back to the kick boxing school in Thailand that licked him into shape in the first series of Adrenaline Junkie. It's a punishing regime of fitness training and learning how to fight, Thai style. Here, Londoner Kai, who has struggled with many of the challenges, comes into his own.