The sun began its descent behind the high dunes of Erg Mhazil.

I hauled myself to my feet, re-shouldered the burden of a heavy pack containing all I needed to survive this week, and left check-point three. One of my bivouac-mates, a serving soldier, army commando and veteran of the Parachute Regiment’s notoriously tough ‘P-Company’ selection, had been forced to pull out at the second of today’s mandatory checkpoints. The skin on his left foot was macerated and separated from the flesh. His injuries were the result of 3 days and around 130 kilometres of running, walking and, occasionally, crawling over dunes, dry wadi-beds and salt flats in temperatures in excess of 40 degrees C.

It made no sense that I was still there. Me! The 58Kg school-teacher. When we were kids, it was my brothers who had been strong and sporty. I was the slight, timid, bookish one. Yet here I was. The Sahara Desert in all its savage glory.

The last few days had been amongst the toughest of my life, and the thought of a further 100 kilometres was hard to contemplate. I felt nauseous. My head pounded. Every square inch of my body ached and then, at the midpoint of the brutal 71 kilometres overnight stage of the Marathon des Sables, I began the ascent into Erg Mhazil.

The sky darkened, revealing the myriad desert stars. I would be blind to their beauty in more ways than one. The light wind blurring the perfect crests of these “Lawrence of Arabia'' dunes hardly hinted at the hellish assault on mind, body and spirit that the night would bring. For years my heavy heart had pined for adventure. Soon I would be truly tested, forced to operate at the very limits of my endurance, from moment to agonising moment, hour after glorious hour.