Something extraordinary happened during a routine walk last week. The walk itself was hardly unusual, aside from the unseasonably fine weather. The route was a well-rehearsed number from our small repertoire of standards; out along Fishponds road up to Eastville park, follow the river to the park's end, then reverse your way back for the return.

It was early in the evening as we set out, and before we had reached the end of our street I realised that I'd left my mobile phone and wallet back on my desk. Although I don't like to leave without either, I reasoned that I didn't particularly need them on this day, and I didn't feel like nipping back. We had the house to ourselves that evening, nobody else would be home until late. Shopping opportunities are fairly limited in Eastville park, so we could probably get by on the couple of coins I had in my pocket.

The dog was having one of those spells when he feels that everything has to be inspected with great care. Every so often this mood catches him and he needs to patiently smell and catalogue things we pass in far greater than usual detail before we can continue. I'm not really sure of the cause of this. It sometimes seems to be precipitated by a change in the weather. A sudden cold snap is certain to bring it about, for example. This evening was not cold at all, although it was unusually humid. So we proceed, at a very leisurely pace, him dawdling with his forensic investigations, me idly speculating about the effects different atmospheres might have upon his primary perception.

One of the more successful methods I've managed to install for regaining his attention, is an ordinary whistle. Over time, via the usual methods of reward and repetition, I've taught him to associate a particular sequence, three short pipes on a whistle, with a food reward. It works well enough to use as an effective recall signal. One of the advantages conferred by a whistle is it's neutral tone; dogs are great readers of context and tone-of-voice can convey a lot of subtext about the caller's intent. Not so the mechanical whistle.

So I keep a selection of whistles bound to my keyring, and on evenings like this, where I am likely to keep striding ahead of the hardworking nasal detective, they can see a lot of action. Even so, we maintained our slower than average pace, we had no reason to hurry.

My fetish for luggage had led me to recently acquire a small Crumpler shoulder-bag, discounted in a shop-sale. I love Crumpler gear. Despite a tendency towards the garish and zany, I think it's well thought out and robustly constructed. I suppose this bag is intended to be a roomy camera case, but I've put it to use as a carry-all for the dog-walking equipment. Recently I had realised there was enough room to stow a tennis ball alongside the rest of the usual baggage, and so when we reached the quiet meadow at the far end of our route we amused each other by throwing a ball around and chasing it for ten minutes.

The dog seemed to have exhausted his investigative enquiries, for on the return route he stayed close to my heel. It was only when we approached the start of the riverside path that he chose to wander into the bushy borders, causing me to reach for the whistle, and realise that I no longer seemed to have it in my possesion. Not only the whistle, I'd managed to lose my entire keyring.

It was one of those moments of precise clarity that can be germinated by a stab of sudden near-panic. All the doors and windows at home were locked, and nobody would be home until perhaps midnight. No telephone, and it's been years since I bothered to memorize any phone numbers. No money either. I was mentally chasing through my limited options.

The best bet would be finding my keys. A large, silver bunch, assuming I'd dropped them shortly after digging out the whistle, I might be able to find them still close to where they fell. Luckily, I'd not strayed from the path, and the park was quiet, I ought to be able to retrace my steps quite thoroughly without rushing to get there before somebody else spotted them.

And so we proceeded, this time with our roles reversed; myself intent, studying the floor and poking into vegetation, him following, curious about my peculiar, unfathomable ways.

As we lucklessly progressed, I did my best to not dwell upon the negative outcome. Slowly we headed toward the end of our searchable area. We'd spent a while arsing about in the meadow, the wilder grass there was eight or more inches long. If the keyring had dislodged as we capered, nothing short of a fingertip search would turn anything up. The keys would lie there, probably undisturbed until the field received it's annual trim, probably next spring. There is a path bisecting the unruly meadow. If I was lucky, they'd have fallen on or near this, and there would be a chance of spotting them

It was not to be. I made a couple of half-hearted sweeps across the grass, roughly in the areas I imagined we'd been running through, maybe an hour previously. I scanned for reflections, or hints of depression that might indicate a dropped weight. It was a hopeless task. Gathering my thoughts, I tried to come up with a scheme to keep myself and an unfed dog occupied and outdoors for the next seven or eight hours. I couldn't be sure that it wouldn't rain.

And then a desperate idea seized me. I looked at the dog, sitting close by, extremely taken by my unusual behaviour. He seemed to be expressing curiosity as to my motive. I dug into my pockets and retrieved the keys to my other house and showed them to him up close. "Find the keys!"

He stuck his nose on the floor and zig-zagged aimlessly across the grass for a couple of minutes, before coming to a halt about twenty yards away. As I went over to collect him, I could see that he was wagging his tail, and staring at the floor.

It wasn't until I was standing right next to him that I could precisely tell that his nose was directly indicating my lost keyring, where it lay hidden beneath the long grass. I was amazed. For his trouble, I emptied out the entire stash of biscuits from my bag, making a small pile.

"Best dog in the world", I say.