He ripped the envelope open, pulling the flap from the grip of the blob of wax that held it firm.

‘Look!’ he said, holding the paper up. ‘The letter is written on the headed stationery of the Diogenes Club.’

‘Check the postmark on the envelope,’ Crowe murmured. ‘What time does it show?’

‘Three thirty yesterday afternoon,’ Sherlock said, puzzled. ‘Why?’

Crowe gazed imperturbably at Sherlock. ‘Mid-afternoon on a weekday, and he’s at his club, writing letters, rather than at his office? Does that strike you as unusual behaviour for your brother?’

Sherlock thought for a moment. ‘He once told me that he often walks across to his club for lunch,’ he said after a moment. ‘He must have written the letter over lunch and got the footman to post it for him. The post would have been collected in the early afternoon, and the letter would have got to the sorting office for around three o’clock, then been stamped half an hour later. That’s not suspicious, is it?’

Crowe smiled. ‘Not in the slightest. Ah was merely tryin’ to indicate that there’s a whole lot of facts that can be deduced from a simple letter. If the postmark had been Salisbury rather than Westminster it would have been unusual, and would have prompted further questions. If we knew your brother never left his desk durin’ the day, not even for lunch – an unlikely occurrence, ah have to admit – and yet the letterheaded stationery was from his club then that would have been unusual as well. You might have surmised that your brother had lost his job, or was sufficiently disturbed that he had not gone into work, or left early.’

‘Or maybe he’d just taken some stationery from the Diogenes Club and was using it in his office,’ Sherlock pointed out.

Crowe looked discomfited. ‘Ah guess there’s always an alternative explanation,’ he growled.