The hardened criminals of Room 83 on the attic floor covered equally satisfactorily the traces of their contraband consignments and the tracks of the consigners. To the outward eye there was not a more innocent-looking room in the whole of the two buildings. But hiding-places lurked everywhere. The floor in this as in nearly every other room was, fortunately, straightforward planking laid without bolts or intersections. Once one plank had been loosened and removed, there was a space about five to six inches deep between the planking and the foundation of the floor wherein to store treasure. When one plank had been removed the remainder could be slid up and down at leisure and the whole of the space filled up, if necessary. This practice was universal, and before the end there was hardly a room without its cache, not one of which, in spite of two or three most conscientious and Berlin-inspired searches, was ever discovered. In this room also there were sliding panels in the walls, false partitions in the cupboards, false bottoms in the drawers. Almost everything that ought to have been solid was hollow. Here maps were photographed without cameras and developed without solutions; German uniforms were made for use if a suitable opportunity arose; an air pump was constructed out of bits of wood and the leather of an R.F.C. flying-coat; air pipes were made out of old tins; a device was thought out to fuse the electric wires outside; dummy keys were fashioned. It was the temple of the Goddess of Flight. Room 24, the little room on the ground floor in B House where the working shifts changed into their orderlies’ clothes, was almost as complete a mask. The clothes themselves were kept unlocked at the bottom of several British uniforms in a wooden box. If a search came they would have to take their chance of being found; it was impossible to “cache” them afresh under the boards every time that they were returned from actual use.