‘In a matter of speaking, since it just so happens I’m a doctor. Only you didn’t make an appointment but I’m nice enough to see you anyway.’

A smile tugged at the corner of her mouth. ‘I’m doing fine,’ she said less defensively.

‘Something happened today,’ I said again.

‘I guess you haven’t talked to Commander Penn.’

‘Not since this morning. I didn’t know you knew her.’

‘Her department’s on-line with us, with CAIN. At twelve noon CAIN called the Transit Police VICAP terminal. I guess you had already left for the airport.’

I nodded, my stomach tightening as I thought of Davila’s beeper going off in the morgue. ‘What was the message this time?’ I asked.

‘I have it if you want to see it.’

‘Yes,’ I said.

Lucy went into her room and returned carrying a briefcase. She unzipped it and pulled out a stack of papers, handing me one that was a printout from the VICAP terminal located in the Communications Unit, which was under Frances Penn’s command. It read: - - -MESSAGE PQ21 96701 001145 BEGINS- - -

FROM:-CAIN

TO: - ALL UNITS & COMMANDS

SUBJECT: - DEAD COPS

TO ALL COMMANDS CONCERNED:

MEMBERS WILL, FOR THE PURPOSE OF SAFETY WHEN RESPONDING TO OR BEING ON PATROL IN THE SUBWAY TUNNELS, WEAR HELMETS. - - -MESSAGE PQ21 96701 001145 ENDS- - -

I stared at the printout for a while, unnerved and inflamed. Then I asked, ‘Is there a username associated with whoever logged on to type this?’

‘No.’

‘And there’s absolutely no way to trace this?’

‘Not by conventional means.’

‘What do you think?’

‘I think when ERF was broken into, whoever got into CAIN planted a program.’

‘Like a virus?’ I asked.

‘It is a virus, and it has been attached to a file that we just haven’t thought of. It’s allowing someone to move inside our system without leaving tracks.’

I thought of Gault backlit by his flashlight in the tunnel last night, of endless rails leading deeper into darkness and disease. Gault moved freely through spaces most people could not see. He nimbly stepped over greasy steel, needles and the fetid nests of humans and rats. He was a virus. He had somehow gotten into our bodies and our buildings and our technology.

‘CAIN is infected by a virus,’ I said. ‘In summary.’

‘An unusual one. This isn’t a virus oriented toward crashing the hard disk or trashing data. This virus isn’t generic. It is specific for the Crime Artificial Intelligence Network because its purpose is to allow someone access to CAIN and the VICAP database.

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

‘And it’s attached to an existing program.’