John ran along beside Sherlock, struggling to keep up and vaguely aware that he probably looked like a Jack Russell trying to pee up a fast moving lamppost.
"Sherlock where are we going?" They had rounded the back of the museum and were now in a wholly unfamiliar and apparently disused area. There were steps going down to a pair of locked and chained doors.
"Down here." John looked and could just make out under several years of city dirt and grime the chipped white tiles that still remained on the red bricks. And part of a red and blue circle.
"The Underground?"
"Not just the Underground John. The British Museum Stations."
"But there aren't any British Museum Stations."
"Not any more but there used to be. There are miles of disused line and a plethora of abandoned stations under the whole of London. Including one that goes right under this museum and the British Museum. Whilst I was checking the vents in the floor I noticed a distinct smell that comes from the particular lubricating oils they use on the wheels of tube trains. Only there shouldn't be any running under the museum."
"So someone is using the old line to travel about?"
"Exactly."
"Well this looks like its still fairly locked. If someone had opened it there would be marks on the floor?" Sherlock smiled. John's deductive powers were coming along nicely.
"We really need to find out what is inside that Dinosaur. It is the key to the whole case. Has to be."
"Mycroft won't tell you."
"Bollocks to Mycroft and his need to know. I need to know. And so do you."
"Well thank you for making me a part of this but I'd rather not get eviscerated by your big brother if it's all the same to you."
"Rubbish. If he wants his bloody Dinosaur back he can just tell us what is so important." Sherlock took off back up the stairs and out onto the street where he flagged down a cab. John just made it.
"Where to mate?" The Cab driver smiled in his rear view mirror.
"The Diogenes Club please."