'We've had another one' Lestrade stated simply, throwing a small amount of case notes across to Holmes, who was perched near the window, looking out onto the street. Catching them adeptly, Sherlock quickly glanced over the images that adorned the front cover.
'Yes it's the same man, though his method is ingenious. If I were any more stupid I'd say he fades from existence, but that can't be it, there's something more.' Sherlock ran a hand through his hair and turned in frustration as he though aloud. 'Seven break-ins, one image stolen each time, none of which are related, aside from them all being slightly blue in colour… and each time he leaves a code behind. This doesn't tie together!'
Lestrade looked over at Sherlock's colleague, John Watson, in surprise. This was the first time that he'd seen the consulting detective confused since they had begun working together, which made the sudden blank in Holmes' knowledge almost baffling.
'Wait… wait… it's an arrangement. Twenty-one numbers, divided by the seven images, leaves three numbers for each image that's been stolen. Take every first and second numbers as grid references, and the third as the image that was stolen… line them all up on a grid…'
Sherlock grabbed several pins and began sticking copies of the stolen images on a pin board decorating Lestrade's office. A halogen light bulb, a blue, wooden garden fence, a Saint John's ambulance badge. As all the images were placed together Sherlock reached the breakthrough he desperately needed – each crime was part of a larger message.
The consulting detective grabbed his coat and scarf and turned to Lestrade.
'Get a couple of cars out looking for a blue police telephone box. 1960's. We find that and we find out thief – He wants to get caught!'
Meanwhile, on a darkened backstreet a few miles away from the police station, the Doctor waited patiently outside his trusty TARDIS. Sherlock wouldn't take longer than a day to find him, and then everything could fall into place.