Right, so at the 17-mile checkpoint, major themes were shade, and foot maintenance. We both topped up with water – going dry out here could be a serious problem – as well as got a some food down our throats. But I also spent some quality time with my feet.

Long-distance walking, one gets attuned to the signs of incipient blisters, which have to be caught early. I'd figured that not walking tomorrow meant I could let them go; but I figured wrong. So – apologising in advance and profusely – I got my feet out of my boots and socks, busted out the Compeed, and got them into action on the blister-in-waiting raw spots.

My other accomplishment here was keeping to the resolution I'd made at lunch. I had been slightly anxious that Tim keep up the moblogging, after I'd alerted people that there would be moblogging. So at the halfway point, as the poor man was just sitting there in the shade trying to catch his breath and eat his sandwich, I wheedlingly said something like, "So, how about a moblog of our lunch spot?" and he said something more diplomatic than I had any right to expect like, "In a minute." Realising what a pain in the ass I was being, I resolved never to hassle him again about that on this walk. Basically, I realised the relationship was a lot more important than a bloody blog post.

So that's why you didn't get any action Compeed-application shots on the moblog.

Compeed applied, a little air on the feet, water topped up, boots laced up tight – good to go! I think these next three photos are beautiful, even if I say so myself.

Using this turn of phrase obliges me to tell Tim the story about when I took Mandy on a bike ride up to Skyline Drive on the SF Peninsula and, as usual, I radically under-reported both the distance and especially the total amount, and steepness, of the climbing, and where Mandy stopped talking entirely about halfway up, and I at this point, mostly through hard experience, was at least smart enough to shut up and just let her do the climb, and but then we got to the top and it levelled off and also these amazing vistas up there opened up, and I ventured, "Now, see, isn't this a wonderful pay-off for all that climbing?" and Mandy replied, levelly, "I have stopped cursing your name surprisingly quickly."

We talk a bit about our awesome walk through the Scottish Highlands. Tim reminds me of something which I've totally forgotten: that I all but promised that I was done walking after that one.

My feet feel a lot better. I suddenly remember reading something about getting one's boots and socks off for a few minutes being a good practice, one which I've never before followed.

I'm kind of in the zone now. My feet and legs still hurt. I'm still panting on the hills. But it somehow has no affective, emotional content. I think I've broken through.

I'm not sure I can say the same, alas, of Tim. He's seems to me to be getting worryingly incoherent. I ask him something, and when he replies, he's speaking in tongues. I try a little monologue just to keep us distracted and keep morale up, but pretty soon even that trails off. We plod on in silence (and blasting sun).

I didn't want to say so at the time, and I hesitate to say it now, but: Tim was starting to look worrying. His face was bright red, slick with sweat – and kind of puffy as well. Taking great care against any implication that anyone might be wussing out, I try to suggest that we can always pack it in. That we don't have to finish. I certainly want to get to the end; but not if securing that objective means taking casualties.

As you'll see from the next three photos, three things happened in rapid sequence.

1. Tim staggered over to the verge and plopped down in the one bit of shade anywhere, which was beneath a thick bush. While I plopped down beside him, he pulled out a bag of crisps and started firing them down. "I don't even like crisps," he said. "It's just for the salt." Seriously.
2. Quelle catastrophe, my pen ran out of ink. Major crisis.
3. One of the event trucks rolled up – and pulled over to see if we were still alive.

We continue to sit in the shade. I try to relate gently to Tim that he is looking worryingly like a heat stroke casualty. We agree that it's nothing to do with stamina, or strength, or certainly with determination. He's simply having a physiological reaction – like altitude sickness. It's just going to happen to you or it won't.

He agrees that he's not dogmatically committed to finishing – he'll quit if he needs to.

Then he gets up and gets walking again.

There's no amusing dialogue from the rest of this section because we were too shagged to be funny; and if we hadn't been, I was too shagged to write it down, plus didn't have any damned ink.

The last checkpoint has the air of an outpost at the edge of the frontier; and the woman running it the manner of a castaway. She seems like she doesn't see other human beings very often.

We mainly talk about the number of Hero Walkers who have dropped out – seven so far, out of a total of 58; and the number who are still behind us, which we're surprised to learn is actually 12. We could be doing worse. We particularly enjoy hearing about the two people who dropped out after four miles.

I probably shouldn't be eating this late in the walk, but it's something to do, other than pant and be exhausted, and in fact I nearly choke to death on a wodge of trail mix, which would have been a funny way to fail.