After exploring London's abandoned tube stations, then taking a pub crawl round the capital, we were beginning to think that Holmes and Watson had somehow got hold of the Minutes from a Londonist editorial meeting. Then, in His Last Vow, the season three finale of Sherlock, the sleuthing duo paid a visit to one of the archetypal 'secret London' locations: Leinster Gardens.
We won't offer any plot spoilers by describing what happened here, other than to say it was the scene in which Mary Watson's face was projected onto a stuccoed west London terrace. Like this:
The houses are quickly revealed to be a facade. Their five-storey fake frontages hide a railway line that passes under Leinster Gardens to emerge behind this point on the terrace. A glorious tracking shot flies over the narrow roof to show the fakery.
This is a genuine location, found at 23-24 Leinster Gardens, mid-way between Paddington and Bayswater. Most passers-by will not notice but, just as Sherlock says, the two houses contain false windows and no letter boxes, as revealed by our video-maker Geoff Marshall.
The facsimile dwellings were built in 1868, after the extension to the Metropolitan Line was cut through the middle of the street. The facade not only restored the continuation of the terrace, but also masked the plumes of steam that passing trains would have vented at this point, upon leaving the tunnel beneath Leinster Gardens.
So effective is the disguise that even locals can be unaware. In his book Underground Overground, Andrew Martin recounts a visit in the late 1990s. He popped into the hotels either side of the anomalous address. The staff were confused, and had never realised why their neighbours were so quiet.
It was a canny location for the Sherlock writers to choose, playing as it does on the title of the well-known Holmes story The Adventure of the Empty House. A house could scarcely be more empty than 23-24 Leinster Gardens. Most sources describe the facade as only five feet thick, making the interior shots from the Sherlock episode unlikely. However, Andrew Martin describes peering through one of two genuine panes of glass and seeing 'a tiny booth-like room containing a chair and a clock stopped at ten to ten'. No sign of the clock, but the description does resemble what we saw in the Sherlock episode.
Most coverage of 23-24 Leinster Gardens suggests that it's been the location of many a practical joke, baffling noviciate delivery drivers for generations. A cutting from the Evening Telegraph of 1935 goes further, suggesting that "a few years ago No. 23 was the scene of unusual commotion when cars containing eminent members of London society drew up to disgorge eager guests for a fictitious garden party announced to be held there". Mary Watson is just the latest in a long line of Londoners to be sent to the empty house.