We walked downstairs very quietly, and did not talk as we threaded the corridors of the seemingly deserted basement. Doctor McNeill unlocked a gray-painted steel door, but it was only a bulkhead leading to a further stretch of hallway. At length he paused before a door marked B 116, opened a small observation panel which he could use only by standing on tiptoe, and pounded several times upon the painted metal, as if to arouse the occupant, whatever it might be.