‘All right.’ Sherlock quickly went over the facts in his mind. ‘In spring your best bet is early morning or late afternoon, and in winter you are better off heading for the market and buying something from the costermonger.’

Crowe laughed. A good summary of the facts, but think about what’s behind the facts. What’s the rule that explains the facts?’

Sherlock considered for a moment. ‘The important thing is the temperature of the water, and the thing that drives the temperature of the water is how hot the sun is and whether it’s shining straight down on the water or at an angle. Think about where the sun is, work out where the water is warm but not hot, and that’s where you’ll find the fish.’

‘Quite right.’

The lure jerked slightly, and Crowe leaned forward, washed-out blue eyes unblinking beneath bushy grey eyebrows.

‘Each fish has a different temperature which it prefers,’ he continued quietly. ‘A good fisherman will combine his knowledge of the fish’s preferred water temperature with his knowledge of the time of year, time of day and lake turnover conditions to work out which fish will be in a particular part of a lake at a particular time of the year.’

‘This is all very interesting,’ Sherlock said cautiously, ‘but I’m not likely to take up fishing as a hobby. It seems to consist of a whole lot of sitting around waiting for something to happen. If I’m going to sit around for a long period of time, I’d rather have a good book in my hands than a fishing rod.’

‘The point ah’m tryin’ to make,’ Crowe responded patiently, ‘in my own countrified, homespun way is that, if you’re tryin’ to catch somethin’, you need to go about it in a structured way. You need to know about the habits of your prey and you need to know how those habits change dependin’ on the local environment and circumstances. The lesson applies equally well to men as it does to fish. Men have their preferences, their preferred locations, at different times of day, and those preferences might be different if the sun’s shinin’ compared with when it’s rainin’, or if they’re hungry compared with when they’re full.