The footpath led us through scrubby woodland to the base of a long line of smooth rock face high above Argentière, which we followed to reach the spectacular rock needle known as the Aiguillette d'Argentière.

Crossing the slopes above Argentière

Here we stopped to look up and take in a deep breath as we studied a series of steel ladders and hand rails heading upwards and out of view - it was the way over the cliffs. As we were taking it all in, a group of French walkers arrived and we deferred the ladders to them, so that we could watch an ascent. It looked much easier than it first appeared and the fair Nello was keen to go, vertigo-challenged me not quite so. Still, you must confront your fears and off we climbed. The fair Nello told me that the views from the ladders directly down into the valley of Chamonix 800m below were quite amazing - I found the views of the rock face itself much more comforting.

However, we left the Grand Balcon as soon as we reached it - our goal was even higher, at Lac Blanc. It was our fourth and last "variante" of the TMB. The path took us up towards the immense rock walls of the Aiguille de Belvedere, past grazing ibex and past the pretty pondages of the Lacs du Chesery, sparkling in their mountain hollows.

A last push up to the snow-line brought us out at Lac Blanc and the refuge of the same name. The wind that cooled us on the ascent now had a distinct chill, so we put on our fleeces and had a cup of hot chocolate, taking in the panoramic views of the turquoise coloured lake surrounded by snow-covered mountain slopes. The ten or so people who were there when we arrived soon grew to a couple of hundred as big groups of French day-walkers began appearing. It was the first Sunday of the summer holidays and France was on the move.

The grand panorama from Lac Blanc - from the Aiguille Verte to Mont Blanc

The turquoise waters of Lac Blanc

After an early lunch, we decided to leave Lac Blanc to the locals and head for quieter pastures, descending via another route to a small pondage to laze on the grass nearby and watch the interplay between cloud and peaks.

Aiguille Verte (4122m)

Unfortunately, the clouds began to take on a distinctly menacing grey tint and the patches of sunlight were becoming rarer. We quickly headed down a rocky goat-track towards the telepherique of La Flegère. It was the source of all the day-walkers, many of whom were still heading up to the lake as we were coming down - it must be one of the most popular day-trips in the area.

Descending the slopes of Les Aiguilles Rouges

As well as a telepherique, La Flegère had a pleasant refuge and it was good to be in early for a hot shower, cold beer and siesta, which was disturbed only by the sound of rain falling on the refuge roof. The clouds had clearly won the day (I hope the day-walkers made it back in time) though by evening a gap had opened in the west, allowing the setting sun to to bathe the peaks and cloud above in a pale pink light - exquisite!

Leaving the refuge at La Flegère, we picked up the track of the Grand Balcon du Sud and followed it southwards, soon dropping down to avoid a series of rock cliffs, before crossing a broad basin split by a section of boulder scree. Across the valley the face of Mont Blanc and its glaciers grew gradually larger, as we began a long and winding traverse of the steep slopes through the coniferous forest and across the small grass prairie of La Charlanon. From here, the track began a steady climb around the now open slopes to the grassy platform of Planpraz, a favourite launching spot for parapentists.

It was fascinating to watch the parapentes take off, drifting slowly out over the Chamonix valley, soaring upwards with the thermals, sweeping gently past forested slopes or crossing distant glaciers, some even vanishing into the cloud above. Cloud? ..... now that wasn't there when we started. Indeed, for the first time, cloud seemed to be forming within the valley itself and rising upwards. When we looked up towards the tops of Le Brevent, where we were headed, they were fast disappearing into the developing mists.

The reverie of flying with the parapentes evaporated as fast as the cloud didn't and we headed quickly on, climbing up the steep rocky track that wound its way up to the heights of the Col du Brevent.

By the time we reached the snow-covered saddle we were enveloped in the cold mist of swirling cloud. A small group of walkers had formed at the col, and we found ourselves as part of a convoy for the climb up to the peak of Le Brevent itself. A short steep pinch up the soft snow brought us to the northern face of the mountain and a further traverse across a steep snow drift and down through a snow- and boulder-filled hollow surrounded by towering rocky knobs.

Crossing a snowy slope at the back of Brevent

It was a fascinating crossing, made even moreso by the fact that the cloud spilling over from the farside valley was dispersing rapidly, offering curious views of the rocky surrounds and the distant sun-filled valleys.

Out of the corner of an eye, we noticed small dark sihouettes moving on the rocky ridge above us - a family of sure-footed ibex were watching us trudge by on the snow below - was it with amusement or disdain, I wondered.

Crossing ibex country at the rear of Le Brevent

A steep final climb over a series of drifts and rocky ribs, with one small section of ladders and rails, brought us to the top of Le Brevent and back into the cloud. Today, it was not a place to hang around for the views, so we started our descent on the southern side almost as soon as we arrived. We had climbed over 11,000m since starting out on the TMB and from here it was all downhill - 1500m down, down, down to Les Houches.

The view from the top of 2520m Le Brevent - it is one of the most spectacular on the TMB (but perhaps not in a fog)

From the peak, the track wound its way down an impressively steep slope of boulder scree, tinted grey and pink and marbled with green lichen. We were soon below the cloud layer and found ourselves crossing a barren rocky bowl that cradled the still blue waters of Lac Brevent.

Passing the lake, we rejoined the long crest of the range from where we could once again admire the immense panorama across the valley, from the Aiguille Verte to the snowy dome of Mont Blanc itself. We may have missed the view from the peak, but from this vantage point it couldn't have been much less impressive.

The last 2½ hours and 1100m of descent were just a necessary job to complete the loop, descending rapidly at first on an endlessly zig-zagging track in a very steep basin, then down through fir and occasional birch forest, across a small ravine and more coniferous forest to reach an enormous concrete statue of Christ-Roi - blessing the people of the valley, but looking away from the humble TMB walkers.