I didn't realize at first that Mr. Crepsley was following someone. He was hovering above a busy shopping street, where he'd been for almost an hour, studying the shoppers. Then, without warning, he climbed to the top of the building he'd been clinging to and started across the roof.

I called Evra. He never called me, for fear the vampire would hear my phone. "He's on the move again," I said quietly.

"About time," Evra grumbled. "I hate it when he stops. You don't know how cold it gets, standing still down here."

"Go get something to eat," I told him. "He's moving pretty slowly. I think you can take five or ten minutes off."

"Are you sure?" Evra asked.

"Yeah," I said. "I'll call you if anything happens."

"Okay," Evra said. "I'd love a hot dog and a cup of hot chocolate. You want me to pick something up for you?"

"No thanks," I said. "I'll keep in touch. See you soon." I hit the off switch and started after the vampire.

I didn't like eating stuff like hot dogs, burgers, or French fries while tracking Mr. Crepsley: his nose could easily detect such strong scents. I ate dry slices of bread - which produced almost no smell - to keep my hunger down. I had ordinary tap water in a bottle to drink.

After a couple of minutes I got curious. The other nights, he'd either stayed in one spot or wandered around without direction. He was moving with purpose this time.

I decided to get closer. It was dangerous, especially since he wasn't rushing - he was more likely to spot me - but I had to see what he was up to.

Closing the gap by a third - as near to him as I dared get - I saw that he was sticking his head out over the edge of the roof, keeping a watch on the street below.

Looking down at the well-lit street, I couldn't spot who he was after. It was only when he paused above a lamp that I noticed the fat man at the base, adjusting his shoelaces.

That was it! Mr. Crepsley was after the fat man! I knew by the way the vampire stared, waiting for him to tie his shoelaces and move on. When the fat man finally stood up and started walking again, sure enough, Mr. Crepsley followed.

Taking a few steps back, I called Evra.

"What's up?" he asked. I could hear him munching on his hot dog. There were voices in the background.

"Action," I said simply.

"Oh, hell!" Evra gasped. I heard him dropping the hot dog and shuffling away from the people behind him, to a quieter spot. "Are you sure?" he asked.

"Positive," I said. "The prey has been sighted."

"Okay," Evra sighed. He sounded nervous. I didn't blame him - I was nervous, too. "Okay," he said again. "Give me your position."

I read out the name of the street. "But don't rush," I told him. "They're moving slowly. Stay a couple of streets back. I don't want Mr. Crepsley spotting you."

" Idon't want him spotting me either!" Evra snorted. "Keep me up to date."

"Will do," I promised. Clicking off the phone, I started after the pursuing vampire.

He trailed the fat man to a large building, which the human disappeared into. Mr. Crepsley waited half an hour, then slowly circled the building, checking on windows and doors. I trudged along behind, keeping my distance, ready to race after him if he entered.

He didn't. Instead, when he was through examining the place, he went to a nearby rooftop, from where he had a perfect view of all the entrances, and sat down to wait.

I told Evra what was happening.

"He's just sitting there?" Evra asked.

"Sitting and watching," I confirmed.

"What sort of place is it?"

I'd read the name on the walls while I was passing them, and seen in a couple of the windows, but I could have told Evra what went on in the building just by the foul smell of animal blood in the air.

"It's a slaughterhouse," I whispered.

There was a long pause. Then: "Maybe he's just here for the animal blood," Evra suggested.

"No. He would have entered by now if that was the case. He didn't come for the animals. He came for the human."

"We don't know that," Evra said. "Maybe he's waiting for it to close before going in."

"He'd have a long wait," I laughed. "It stays open all night."

"I'm coming up," Evra said. "Don't move until I get there."

"I'll move when Mr. Crepsley moves, whether you're here or not," I said, but Evra had hung up and didn't hear me.

He arrived a few minutes later, his breath stinking of mustard and onions. "Dry bread for you from now on," I muttered.

"Do you think Mr. Crepsley will smell me?" Evra asked. "Maybe I should go back down and -?

I shook my head. "He's too close to the slaughterhouse," I said. "The smell of blood will block everything else out."

"Where is he?" Evra asked. I pointed the vampire out. Evra had to squint but eventually spotted him.

"We have to be extra quiet," I said. "Even a small noise could have him swooping down on us."

Evra shivered - whether because of the cold or the thought of being attacked, I don't know - and settled down. We said hardly anything to each other after that.

We had to breathe into our cupped fists to stop our breath from showing. We would have been all right if it had been snowing - the snow would have hidden the smokelike tendrils - but it was a clear and frosty night.

We sat there until three in the morning. Evra's teeth were chattering, and I was at the point of sending him home before he froze to death, when the fat man emerged. Mr. Crepsley started after him immediately.

Too late, I realized the vampire was going to pass by us on his way back. There was no time to hide. He'd see us!

"Keep perfectly still," I whispered to Evra. "Don't even breathe."

The vampire came toward us, walking steadily across the icy roofs in his bare feet. I was certain he'd spot us, but his eyes were trained on the human. He passed within ten feet of us - his shadow crept over me like some awful ghost - and then he was gone.

"I think my heart stopped," Evra said shakily.

I heard the familiar thump-thump sounds of the snake-boy's heart (it beat slightly slower than a normal human's) and smiled. "You're okay," I told him.

"I thought we were done for," Evra hissed.

"Me, too." I stood and checked which way the vampire was going. "You'd better slip back down to the street," I told Evra.

"He's not going fast," Evra said. "I can keep up."

I shook my head. "There's no telling when he'll speed up: the man might get in a cab or have a car waiting for him. Besides, after our narrow escape, it's better we split: that way, if one of us gets caught, the other can sneak back to the hotel and pretend he wasn't involved."

Evra saw the sense in that and went down the nearest fire escape. I began following the tracks of the vampire and the fat man.

He walked back the way he'd come, past the deserted street where we first picked him up, on to a block of apartments.

He lived in one of the central apartments on the sixth floor. Mr. Crepsley waited for the lights to go off inside, then went up in the elevator. I ran up the stairs and watched from the far end of the landing.

I expected him to open the door and enter - locks were no problem for the vampire - but all he did was check the door and windows. Then he turned around and went back to the elevator.

I hurried down the stairs and got the vampire back in view as he walked away from the apartments. I told Evra what had happened and where the vampire was heading. A few minutes later he caught up with me and we followed Mr. Crepsley as he jogged through the streets.

"Why didn't he go in?" Evra asked.

"I don't know," I said. "Maybe there was somebody else there. Or maybe he plans to come back later.

One thing's for sure: he didn't go up there to send a letter!"

After a while, we turned a corner into an alley and spotted Mr. Crepsley bent over a motionless woman. Evra gasped and started forward. I caught his arm and yanked him back.

" What are you doing?" he hissed. "Didn't you see? He's attacking! We have to stop him before -?

"It's okay," I said. "He isn't attacking. He's feeding."

Evra's struggles stopped. "You're sure?" he asked suspiciously.

I nodded. "He's drinking from the woman's arm. The corpses in the building had their throats cut, remember?"

Evra nodded uncertainly. "If you're wrong..."

"I'm not," I assured him.

Minutes later, the vampire moved on, leaving the woman behind. We hurried down the alley to check. As I'd guessed, she was unconscious but alive, a small, fresh scar on her left arm the only sign that she had been feasted upon.

"Let's go," I said, standing. "She'll wake up in a few minutes. We'd better not be here when she does."

"What about Mr. Crepsley?" Evra asked.

I looked up at the sky, estimating how long was left until dawn. "He won't kill anyone tonight," I said. "It's too late. He's probably heading back for the hotel. Come on - if we don't get back before him, we'll have a hell of a time trying to explain where we were."