If she were to volunteer to sort the laundry it should be easy to borrow a food scientist's white coverall, cap and face mask. As soon as no one was watching she would slip into a washroom, put on the whites and, completely disguised, walk past the yeast vats to the Door.

“I'll do it!” Almost happy again at the thought of action, she ran along the path to the elevators and went downstairs to join her class.

Two hours later she was walking, with as much authority as she could muster, past the yeast culture tanks and vats, towards the western wall. Getting the clothes had been easy. No one ever wanted the job of sorting the smelly overalls used on Floor One. When the sorting was finished, she had carried the bundles to the washing machines and then quietly left.

She looked around her quickly. She mustn't seem unsure of what she was doing, or some officious person would be bound to come up and ask if they could help. Close up her disguise would be useless.

There were half a dozen doors in the western wall, all apparently the doors to storerooms. There seemed to be no Door with a capital D. Well, she would just have to explore and hope she found the right one before someone noticed her.

The first door led to a room lined with shelves filled with dormant cultures. Door number two led to a store of miscellaneous equipment, spare glass vats and tubing. She opened door number three. Her heart was thudding noisily and she could feel the sweat running down her flee behind her mask. Surely someone was going to notice her peculiar behaviour.

The room was cluttered with cleaning supplies. Propped against the back wall was a step ladder. She was just about to close the door when she noticed, through the rungs, the outline of another door. A door with great bolts top and bottom!

Ruth slipped into the room and closed the door behind her. Her hands were shaking as she moved the ladder out of the way. If she could open the Door it would be a sign that she was doing the right thing, she told herself, that she was supposed to leave the Ark. She grasped the bottom bolt with both hands. It was stiff with age and wouldn't budge. She wiggled it up and down and pulled again. At last it relented and shot back with a loud thunk.