Two days previous

Colon and Nobby were on patrol again even though they had a case that needed to be solved. This morning Commander Vimes had told them that Sergeant Angua would be assisting them, or rather, taking over the investigations, while the two of them assisted her. It didn't make much sense for Colon though, since he considered the case closed.
"You see, I don't get it. That vampire killed the girl, because he got hungry, and now he's dead as well. What else is there to know about it?" he announced, while they bypassed a parked cart.
"I think the commander wants to know who killed the vampire," Nobby offered carefully.
"Yeah, but why? He was a killer after all, shouldn't we just call it luck and forget about it?" Colon argued. He would not let himself get talked into believing that these further investigations were not unnecessary effort that easily.
"But somebody murdered him, and a crime is still a crime, even if the victim is a criminal himself, otherwise we would have little work to do in a city like this. Isn't that what the commander said?" Nobby asked, apparently curious, but even still Fred couldn't help considering the remark to be somehow smartass.
"Who tells us that this isn't some strange kind of suicide, after all? Maybe he just couldn't stand what he had done and brought justice upon himself."
"It's a fair question, but how was he supposed to put so much distance between his head and his body?" Nobby argued, all the while seeming completely oblivious to the fact that he was, in a way, outsmarting the sergeant. "I mean, a headless vampire can't walk through the whole city, least of all unnoticed."
Colon grumbled. He liked it much better when Nobby went along with the things the sergeant said. The corporal wasn't supposed to be the smart one.
"It could have been some pranksters, who thought it would be funny to mess with the watch."
"That's very likely," Nobby said enthusiastic, still not noticing the sergeant's discomfort. "Certainly more likely than some conspiracy going on."
"See, that's what I've been thinking all along," Colon said, victorious.

"This is quite a challenge," Cheery said miserably, as she rounded the crime scene for the fifth time in about an hour.
"Tell me about it," Angua sighed, rubbing the bridge of her nose.
It wasn't easy to find any useful evidence in a place like this. Hundreds of people made their way through the Gates each day and every single one of them left both visible and invisible evidence. Try as they might, both Angua and Cheery were not able to tell the relevant and the irrelevant traces apart.
"Is there anything you can say about the way the body got here? I only found wheel tracks from several carts and carriages, but they could have been here before the body was cast-off, and those footprints... it's such a mess, I couldn't even find two matching ones yet!" Cheery said annoyed.
Angua sniffed the air again, although she already knew the answer to Cheery's question. It was an instinct to try again, even though it was useless.
"Well, I can smell the vampire and something isn't right with the way he smells, but I'm not sure what it is. There are so many other scents covering it up. It could be the scent of another vampire, although that one could have just been passing by. I mean, there's no law against vampires leaving or entering the city. Or I'm mistaken after all," Angua shrugged, trying to battle down the headache she had developed while trying too hard to find something that possibly wasn't even there.
"Can you follow the track of the dead vampire?" Cheery asked hopefully.
"Not really, no," Angua answered harsher than she had originally intended to. Quickly she tried to apologize without actually having to. "It's complicated, because... well, normally a scent is like a long line, that slowly fades, but this one, it's more like... I don't know, a circle maybe. There is no way to tell where it came from, or where it went."
Cheery's brows furrowed, thinking through the same problem, Angua had been dealing with for some time already. "You think he was dropped here, like something flew by and dropped him?"

"Possibly," Angua admitted, "though I'm not sure what could possibly carry that much weight while flying. Vampires can change into bats, but I doubt that anyone could have enough self-control to organize all the bats that would be needed to carry such a weight."
They stayed silent for several minutes, while they both tried to detect something they might have missed during their first fourteen tries, Cheery with her eyes, Angua with her nose.
"What if the murderer was a human? Can you compare the smells of the two crime scenes to each other, so we can tell if someone was at both of them?"
Angua had to admit that it was a fair question, but she knew the truth about the landscape of smells she was offered. There were limits to a werwolf's abilities as well and she currently found herself at their rim.
"That's very unlikely, since there are just so many smells in this place. On the other hand, I think there's something else I can do. We already have a suspect, so why not have a look at him? If the girl's father actually killed the vampire I can smell it, even if he has tried to wash it off."
This was the only thing she could come up with without redefining the word "impossible".

While Angua and Cheery were inspecting the crime scene, Commander Samuel Vimes had other things to worry about. Well, more precisely one thing, and if one was to be really precise, one person. He was about to have a meeting with the Patrician and there was no doubt the vampire case would be mentioned. The commander knew that he couldn't offer much success concerning the investigations. Sergeant Angua had talked to the dead girl's family, but as far as he knew the father had been with his family and they were all assured that this was actually the truth. The watch was currently at a loss, which wasn't good considering that it was a very sensitive topic they were dealing with.
Vetinari had been as neutral and calm as ever during their talk so far, but Vimes could tell that he was standing on thin ice.
"I hope that you are aware of the seriousness of this situation, commander," Vetinari said.
"Sir," Vimes answered, keeping his stony expression up as a form of protection. Damn, he could never look at Vetinari again without remembering their moment in the monastery. At any rate, it wasn't making things easier.
"The last thing the city needs right now is a war between species," the patrician went on. Vimes forced himself to concentrate on the matters at hand again. He contemplated using another "sir" as an answer, but the ice was already thin enough and he didn't want to fall into some kind of metaphorical scorpion pit.
"My best men are already investigating this crime, sir."
Vetinari raised one eyebrow. "Fred Colon and Nobby Nobbs?"
Battling the urge to shift uncomfortably, Vimes replied, "Sergeant Angua has taken over the investigations; those two are only assisting her."
"If you think that is the right move, I'm not going to argue," Vetinari said as if he didn't care, but his next words were heavy. "You should know, though, that this is serious issue and that I trust you to solve this case as quickly and inconspicuous as possible."
Vetinari didn't say more, but Vimes could hear the silent threat that followed his words.
"Of course, sir," he said, still not taking his eyes off the spot just above Vetinari's head.
Their talks were never long and they never actually discussed anything. Every important part of their conversations was passed silently between them. This time, though, Vimes didn't need to be reminded of the importance of the situation they were in. The whole city was heading for trouble if those murders weren't solved soon.

The previous day

Angua had visited the baker yesterday, trying to detect a vampire's scent on him, but the man had smelled of nothing but human, grief, flour and baked goods. It must have been days since that man was last near a vampire at all. To make sure she had missed nothing, Angua talked to the other family members as well, but none of them provided any new information.
There had been one interesting discovery she could make, though. The girl's room had smelled of vampire, even though that smell had already been several days old as well. However, there had been something wrong with the vampire's smell, the last time he had visited. It was the same faint kind of wrongness she had detected at both crime scenes. If only she could tell what it was!
The dominant smell of vampire made it hard to make out any further details, but after having visited the girl's room Angua knew what the dead vampire was supposed to smell like. He had visited the girl on a regular basis, which was very interesting indeed. Angua wasn't sure what to think about this.
As Angua arrived at the watch-house this morning, she found a message on her desk. It was short, made up by only a few words.
Butchers Guild. Please hurry.