Amongst the true elite of the modern commandos are the Mountain Leaders. Known simply as the Cadre, they are the reconnaissance force of the Royal Marines, mountain and Arctic warfare specialists who are capable of operating deep behind enemy lines.We follow Oli, who has always dreamed of becoming a member of the Cadre ever since he joined the Royal Marines five years previously. He had to come off an earlier course due to injury, and we join him as he faces brutal conditions, including a month-long climbing selection phase in Cornwall, three weeks of survival training on a remote Scottish island during Storm Arwyn and a 200km trek in the frozen north of Norway.