Evening was falling in a reverential hush over Whitehall.

It took some apartments by surprise, but here the discreet lamps were already glowing. Their mellow light flowed across polished mahogany and gleamed knowingly on brass, while on the priceless sixteenth-century side-table beside the Louis XV writing desk it brought up the hundred subtleties of the intarsia surface.

Other apartments were stridently modern, wildernesses of chrome and monochrome. This one rejected such crass hommage to the prevailing winds of fashion. The velvet nap of the chair at the writing-table glowed darkly crimson as the heart of the fine Cabernet Sauvignon that stood in crystal at Mycroft Holmes's elbow, and the sumptuously embroidered folds of the curtains at the window hung with studied artlessness across the last of the waning light. Behind the panes of the bookcase in the corner, gilt titles gleamed on leather spines.

The butler entered, his presence as insubstantial as a ghost. The folder that presently materialised on the left arm of the deeply padded velvet armchair could have coalesced out of the ether, for all that was made of its arrival.

Haste would have been entirely unseemly. The hands of the lacquered clock half-seen in the shadows had moved on a little before the folder was lifted without hurry to slide out the contents.

There was not much: a photograph (reasonably good quality) and a printed document that contained far more than the subject of it would probably imagine could be of the remotest interest to Her Majesty's Government.

The armchair was placed near enough to a nearby table lamp for the document to be easily read, even in such low lighting conditions. The apartment's owner was infinitely experienced in picking out the relevant information from reams of text, and this file yielded up its secrets in something under thirty seconds.

The evening was warm. As a result, the window in the bedroom stood slightly ajar, and it was no surprise that presently a small form slipped noiselessly around the door and strolled with studied elegance across the Persian carpet.

Pets were not permitted in the apartments. Nor would Mycroft have tolerated the inevitable concomitants – food bowls, litter trays and (horror!) pet hair. Nevertheless, this was not the first time this arrogant visitor had made free to enter, and something about the superbly aloof poise of the animal made the elder Holmes briefly tolerant, as one beholding his own image.

The cat leaped lightly onto the table beside the lamp and sat down, placing each paw with aristocratic care and curling a whip-thin tail around all. Jewelled blue eyes were set in an onyx mask.

Petting was neither offered nor attempted. They were both far too fastidious for that.

"So, what do we think?" Whimsically he tilted the photograph so that it could be shared. "Watson. Doctor John Watson. Served in Afghanistan, wounded, honourable discharge. Tediously respectable."

The cat blinked disdainfully at the photograph of Doctor John Watson.

"Ye-es. I tend to agree." He restored the picture to the folder and glanced briefly at the file before slipping it back inside. Nevertheless, after a moment he brought out the photograph for a second time.

What was there in that to keep him studying it? No distinction of feature, no stylishness of dress; nothing but a very ordinary Englishman captured crossing Oxford Street, a frown that might be concentration or pain or both sunk between the brows of a very ordinary face.

Once again he moved to restore the picture to the folder, and again withdrew it. The cat watched him with cool incredulity, but however Mycroft might deride instinct as opposed to intellect, even he occasionally admitted that it had its uses – particularly his own.

"Well." He pursed his lips. "Perhaps we may be advised to just have a little word."

This was clearly felt to be excessive. The small mouth just opened on an almost soundless mew.

"I know, I know. You feel I worry too much. But then, you don't know Sherlock." He picked up the glass of wine and looked at the cat over the top of it. "Since I do, I'm inclined to – err on the side of caution, shall we say?"

His feline visitor declined to comment. It sat, silently disapproving, as Mycroft lifted the telephone and issued his orders.

The limousine would be at the door in five minutes.

He sighed. It had been a long day, and he'd been looking forward to reading some reports that had just arrived in an anonymous diplomatic bag. But there was no help for it: family came first, however tiresome the position of an elder brother might be.

The photograph was still lying atop the folder. A very ordinary Englishman. The sort of man, in short, who'd bore Sherlock out of his much-vaunted wits in a week.

But nevertheless...

"Ridiculous," muttered Mycroft.

The cat, evidently sharing his opinion, leaped lightly down from the table and stalked back into the bedroom, from whence it would doubtless vanish about its own concerns.

But when the door closed behind Mycroft Holmes, departing on a fool's errand, the photograph was still on top of the folder, resting where it had been placed on the priceless sixteenth-century side table: a picture of a very ordinary Englishman.

The End.