This virus is like a master key. It opens up every room in the house.'

'And it's attached to an existing program.'

'You might say it has a host,' she said. 'Yes. Some program routinely used. A virus can't cause its damage unless the computer goes through a routine or subroutine which causes a host program - like autoexec.bat in DOS - to be read.'

'I see. And this virus is not embedded in any files that are read when the computer is booted, for example.'

Lucy shook her head.

'How many program files are there in CAIN?'

'Oh my God,' she said. 'Thousands. And some of them are long enough to wrap around this building. The virus could be attached anywhere, and the situation is further complicated because I didn't do all of the programming. I'm not as familiar with files others wrote.'

Others meant Carrie Grethen, who had been Lucy's programming partner and intimate friend. Carrie had also known Gault and was responsible for the ERF break-in. Lucy would not talk about her and avoided saying her name.

'Is there any possibility this virus might be attached only to programs Carrie wrote?' I asked.

The expression did not change on Lucy's face. 'It might be attached to one of the programs I didn't write. It might also be attached to one I did. I don't know. I'm looking. It may take a long time.'

The telephone rang.

'That's probably Jan.' She got up and went into the kitchen.

I glanced at my watch. I was due down in the unit in half an hour. Lucy placed her hand over the receiver. 'Do you care if Jan drops by? We're going running.'

'I don't mind in the least,' I said.

'She wants to know if you want to run with us.'

I smiled and shook my head. I couldn't keep up with Lucy even if she smoked two packs a day, and Janet could pass for a professional athlete. The two of them gave me the vague sensation of being old and left in the wrong drawer.

'How about something to drink?' Lucy was off the phone and inside the refrigerator.

'What are you offering?' I watched her slight figure bent over, one arm holding open the door while the other slid cans around on shelves.

'Diet Pepsi, Zima, Gatorade and Perrier.'

'Zima?'

'You haven't had it?'

'I don't drink beer.'

'It's not like beer. You'll like it.'

'I didn't know they had room service here,' I said with a smile.

'I got some stuff at the PX.'

'I'll have Perrier.'

She came over with our drinks.

'Aren't there antivirus programs?' I said.

'Antivirus programs only find known viruses like Friday the Thirteenth, the Maltese Amoeba, the Stoned virus, Michelangelo. What we're dealing with inside CAIN was created specifically for CAIN. It was an inside job. There is no antivirus program unless I write one.'

'Which you can't do until you find the virus first.'

She took a big swallow of Gatorade.

'Lucy, should CAIN be shut down?'

She got up. 'Let me check on Jan. She can't get through those outer doors and I doubt we'll hear her knocking.'

I got up too and carried my bags into my bedroom with its plain decor and simple pine wardrobe. Unlike other rooms, the security suite had private baths. Through windows I had an unspoiled view of snow-patched fields unrolling into endless woods. The sun was so bright it felt like spring, and I wished there were time to bathe. I wanted to scrub New York away.