Mike lies sprawled on the sandy track as I come up over the rise.

Someone is trying to make him stand. He looks reluctant, but seems to be contemplating it.

"Just stay still, bro!" I shout as I pull off my helmet, sweat from the scorching sun beading across my forehead. Misha does the same. I squat beside Mike.

"Tell me what happened, bro." He doesn't say much, but the defeat in his eyes speaks for him.

"I heard a popping sound," he mutters, "just like last time I broke my leg."

The others resign themselves to a long wait in the fiery heat while Mike and I make the bumpy 30 kilometre jeep ride back to the nearest town. It takes several minutes to ease Mike into the backseat, which is crowded with the luggage of the young German couple who had hired the vehicle. They wait with the others while their driver and translator come with us.

The jeep is hot and stuffy. Dirty windows smeared with dust make it nearly impossible to see outside, and small signs designating the jeep as a "tourist" vehicle are taped over the glass.

On of Britney Spears' early singles is blaring from a cassette tape through static-ridden speakers, and the young female translator sings along. The driver, a curly-haired man with a moustache, sits expressionless as he guides the jeep over large bumps and steep gullies at tremendous speeds. He looks faintly bored.

The stress and tension of the previous week catches up on me. Mike is the third member of the team to be facing a flight home in a week: First Tom's engine appeared to have lost a bearing, and then Misha had sprained his ankle badly, possibly fracturing it.

I cry. In the bouncing, juddering jeep, I wipe hot tears away from under my sunglasses.

"You can't do this, bro!" I say to Mike, half in despairing anger, half in sadness at what I know to be inevitable.

"You can't break your leg!"

Collected as ever, Mike slides his sunglasses down to guard against stray tears himself, and says, "Don't get me started, bro."

As we catch sight of the town, I see a large, prison-like building that is disintegrating, slowly. A vivid thought enters my head: I hope that isn't the hospital.

It is.

Mongolian doctors and nurses look on with mild interest as we help Mike across the broad, gritty courtyard, but they do nothing to help. Each step is like a dagger driven into Mike's leg. In a grand gesture to impracticality, the entrance to the hospital is located up a large flight of steps, each a different size and unevenly spaced.

The wooden door is closed, blue paint peeling off in thick strips.

"You want the good news or the bad news?" I ask Mike.

"The good news is, you're nearly up the stairs. The bad news: there's another flight of stairs inside."

Mike refuses the second set of stairs, plonking himself down in defiance and insisting a doctor come to him, not the other way round.

We wait for ten minutes in a hall coloured an unhealthy shade of blue before a short, chubby Mongolian with a wispy moustache and a look of pure arrogance shuffles down the stairs, ignoring Mike.

We yell for the doctor to come back, sure he hasn't seen Mike, but he beckons for Mike to stand and follow him into an examination room.

People say hospitals smell of disinfectant. I wish this one did, but it doesn't have any. It has no running water either - nurses are constantly being sent with two large pails to gather water from the town well.

The examination room is no better: we have to lift Mike over a pipe that's been fixed in the doorway, ten centimetres above the ground.

The room is bare, decorated only with two medical charts donated by Japan, several medical gowns, a chair, and a single lightbulb dangling from a frayed wire.

Without asking any questions, the doctor kneels down and roughly squeezes Mike's leg, causing Mike to double-up in agony. It is nearly the doctor's last examination - I have to restrain Mike from hitting the man. After fifteen seconds of hard prodding, the doctor stands and announces his verdict.

Pointing at the large mound of bone pressing unnaturally against Mike's skin, he says "not broken, just sore".

He recommends an x-ray, although, unsurprisingly, there is no such facility at the hospital.

We will need to travel 200 kilometres to Uliastay in the hope their x-ray machine is working.

The ride to Uliastay does not begin well. The driver we arrange for Mike's motorbike first turns up with a van, confident that he can squeeze Mike's bike inside. At our insistence, he returns with a flat-deck truck, but no rope. Further persuasion produces one rope after another 40 minute wait. Resigning ourselves to the less-than-ideal situation, we jump in, and Mike's trial over the rutted tracks begins again.

Each time the truck bounces over a large bump, the driver looks at Mike with an anxious expression and his hands leave the wheel as he give Mike an inquisitive "thumbs-up".

We follow the truck on our bikes, riding into a sunset brilliant with colours against the surrounding mountains. I feel guilty for admiring the beauty of the moment. It quickly becomes apparent that we won't make it to Uliastay that night, so the driver stops at a small hut on the side of the track that looks deserted.

He rouses the local host from her sleep and she appears, bleary-eyed, to cook us a soupy bowl of meat, fat, gristle and noodles. I stare into my dish, slightly nauseated, before hungrily finishing it.

All five of us are supposed to sleep on one large, stained mattress, so Tom, Climo and I volunteer to pitch our tents next to the bikes.

The next morning begins at 5am, with the driver rousing himself noisily. The truck sets off before us, as we are confident of catching up easily. Riding is treacherous but reverent, sandy trails winding through mountains that soar like sea-chop crystallised in mid-break.

Climo gets his first flat tyre about 150 kilometres from Uliastay.

Misha is looking after Mike in the truck, and has taken the puncture-repair equipment with him. All we have is two small patches, a tiny tube of glue and no tyre irons. We make a call: Tom will ride on ahead in the hope of catching the truck, while Climo and I will try and flag down a passer-by in the hope of borrowing a set of tyre irons.

Several hours later, we are sitting on the side of the road again, now 30 kilometres from Uliastay. We haven't heard from Tom, who we guess must have been needed in town.

While we managed to fix the first puncture, and several others since, we are now out of patches, out of glue, and Climo's tyre is flat again.

Raw heat burns down on us, and then we receive a text message: "Mike has broken his leg, and his trip is over."

Devastated, we make another decision: I will travel into Uliastay to find help for Climo, while he waits with his bike in a shady gully.

As I approach Uliastay, I am caught in a sandstorm that claws mercilessly at my bike. I realise I have no idea where the hospital is. Attempts to ask directions from the few people brave enough to venture outside in the storm fail. I am rewarded with a mouthful of grit and eyes full of dust each time I lift my visor. Gaining intensity, the dry storm shakes cars and threatens to tip over a van.

Stumbling into a local cafe, I mime Mike breaking his leg, and while most of the customers look at me as though I am insane, one man's eyes light up in a moment of understanding. We run back outside, and he jumps on Piza with me, in the space that doesn't exist between my bag and my bike, forcing me to sit on my tank, legs splayed forward.

The second hospital is as bleak and impoverished as the first. Mike has the required x-ray, which confirms the worst. Tom has to find the materials for a plaster cast from a nearby chemist, and then pay a doctor to mould it to Mike's leg. The rest of the day is gloomy, miserable and strenuous, as we struggle to reunite and get five bikes and five riders to the security of a small guest-house in town.

We farewell Mike the next day from a dusty airstrip in a wide valley surrounded by barren, rocky crags. Misha and I try to carry Mike onto the plane, but are told we cannot travel past the departure gates.

Bravely trying to hold himself up, Mike slips on the polished floor a few metres from us. Tears in our eyes, and anger blazing at the security guards, we insist on walking him further. We are finally held back at the airstrip, and Mike has to make his own slow, painful way across the tarmac and up the steep stairs into the tiny aircraft.

We arrived in Uliastay as five - five young guys with several months of travel ahead of us. We were a tight unit, a team that had already been tested and had bonded together in loyalty and friendship.

We left as four - and we felt the numb pain that comes from something lost. We continue as four, but know in our hearts that we should be five.

* To help Rob and his mates reach their fundraising target for the Living Hope charitable organisation in Vladivostok and for more information on their journey, click here.