It's the perfect day for a run.
Instead, I climb into my car and drive to the swimming pool.
When I arrive there is a small queue of regulars waiting at the front door to be let in. They fall into two clear categories: the very old, who wake early and come to glide carefully, like small wise turtles, up and down in the slow lane; and the very fit, who leap out of bed to come and motor up and down in the outside pool - the temperature of which is kept seriously cold, for serious people.
Then there's me. I keep telling myself it doesn't matter that I don't fit, because I'm not a swimmer, I'm a runner and I'm only here for a while.
But it's been two months, and that's starting to feel a bit longer than a while.
It's two months since I limped over the finish line of the London marathon and I haven't run since. I've seen a doctor, a physio, and an osteopath. They all have different opinions about what I might have done to my knee. I don't know what to do with so many different suggestions, so I'm not doing anything at all. That's to say - I'm not running. But I think about running every single day. And every day my knee reminds me, in various squeaks and twangs, and the occasional shooting pain if I'm starting to feel too optimistic, that it's not ready to be tested.
But I'm really bad at sitting around. And I want to be fit for when I can run again. So I'm spending a lot of time in the pool.
I don't like swimming. I've written about this before, so I won't bore you with it again, except to say that compared to running through fields of waving grass - and along tracks of fresh-smelling earth, in the fresh air and glorious, isolated, freedom - the up-and-down of the bob-dip-chlorine-sting while avoiding other people's toes and spit is really not doing it for me.
But I am persevering.
This morning, when the gym manager comes to let us all in, she advises that the indoor pool is closed because the chlorine levels are too high, so it's the outdoor pool only. A mutter goes up. I walk to the changing rooms behind three old ladies with candyfloss hair and velour tracksuits who are each dragging a small bag on wheels stuffed with potions and curlers and other, vital, post-swim kit.
"Why are the chlorine levels so high?" one wonders aloud.
"Someone had An Accident in there yesterday," says another, knowledgeably. "A number two."
The third one tuts. "Children in the pool. What do you expect. Really."
"Oh no," says the second one, mildly. "It wasn't a child. It was an adult."
The first one squeaks, and so do I, but manage to turn it into a light cough in time.
We go into the changing rooms. The ladies turn left. I turn right. I open a locker door, and start to get changed, grumbling to myself about being stuck doing the kind of sport so insanitary that you have to be doused in chemicals in order to protect you from other people's poo. I huff and puff, and brace for a cold dip.
But when I get to the door to the outdoor pool, there's a gaggle of disgruntled Serious Swimmers blocking the way with their broad shoulders and tiny waists and lean sculpted thighs. (What? Oh okay, so this sport does have one thing going for it.) It turns out that the outdoor pool is shut too, because the water levels are too low. There's no swimming at all this morning.
Everyone goes back to the changing rooms. I stand alone for a moment, frustrated - reluctant to pack up and go home but unable to think of an alternative. Then the janitor comes past and says he'll be testing the chlorine level of the indoor pool again in ten minutes and why don't I go to the steam room for a bit and then come back. So I do.
When I re-emerge, pink and blinking, the janitor gives me a cheery thumbs-up. The pool is open and I am the only person there. I rush to it and dive in immediately, suppressing a whoop, and strike out.
By the fifth lap I realise that I am smiling to myself in the way I used to when a run was going really well. By the tenth lap I realise that I didn't think about the last five laps because I was enjoying myself so much. By the twentieth lap I become aware that no part of my body is hurting me, at all, and that this is the first time in weeks and weeks that I have felt so whole and healthy. By the twenty-fifth lap I feel as though I am becoming longer and stronger. By the fiftieth lap, I have abandoned all conscious thought, lost in blissful blue zen.
After seventy laps I stop and surface and shake my head and clean my goggles. Then I do a quick back flip under water in quiet celebration. I haven't felt this good in a long time. I could keep swimming for ever, but a glance at the Olympic clock on the wall tells me I have to go home.
I pull myself out and glance around, and realise that I'm no longer alone. There's a man at the other end of the pool, in the lane beside mine. He isn't swimming, but is squatting in the water so that it comes up to his shoulders and the tip of his luxuriant beard, which I see now that he appears to be grooming.
I suppress a shudder and go for a very hot shower. But I'm already planning when to come back again.
I will be swimming a mile for autism on Sunday July 20, as part of a nationwide campaign to raise awareness. You don't need to sponsor me - but do join in. It's easy. Simply:
- Do a mile in whatever way you choose - walking, cycling, running etc.
- Post your #AMileForAutism photo to Twitter or Facebook on 20 July (not forgetting the all important hashtag!)
- Text AMFA14 and either £1, £2, £5 or £10 to 70070 to make a donation, then encourage friends to join in and do the same.
Click here for more details.