Part 1: It's Grim Down South (London)

"There's always been something about a fishmonger's shop," said Brian Lane, "that I just can't abide."

Jack Halford looked up from the sports pages of his newspaper. He shot a knowing glance over at Gerry Standing, who was sitting at his desk in the corner like a man who'd never heard of wordplay, and then looked back at the speaker.

"Really, Brian?" said Jack. "So what is it you've got against fishmongers, then? The fishy smell? The lurking fear that anything you buy there might send you straight to hospital with a nasty case of food poisoning?"

"Or just the great long queue and the fact they never have any cod nowadays because of the ruddy fishing quotas?" chimed in Gerry, feet up on the desk as he checked yesterday's racing results.

"None of those, really," said Brian. He leaned forward, as if he were about to impart some highly confidential information. "It's the fish themselves, you see. I just hate all those scales, and the slimy feel of the skin and the dead empty eyes. Bbbrrr…those things creep me out! And don't even get me started on shrimp and prawns…crustaceans. You know, they're just like insects living in the sea, but for some reason we're fine with eating them. I mean, you wouldn't eat a woodlouse, would you?"

Jack and Gerry snickered. "Honestly, Brian, whatever next?" said Gerry. "A phobia about seafood – is that your latest symptom? I hope you're taking all your meds." A tone of genuine concern crept into his voice. Much as he and Jack liked to tease Brian about his eccentricities, they knew the score about his mental illness and what a mess it could leave him when it genuinely kicked in. Especially when that involved him actually going off his medication.

"Oh, I'm fine, don't worry about me," replied Brian. "It's just…I don't like fishmongers. Or what they have on sale."

"Nothing like a nice bit of fish with a few chips," said Jack, disapprovingly.

"Well, I can see you guys obviously don't have enough work to do right now," broke in the voice of Detective Superintendent Sandra Pullman, as she stalked into the office. "Gerry, please get your feet down off that desk, if I've told you once I've told you a thousand times. Thank you. Right, if you're finished with the chit-chat about fish, then you'll be pleased to hear that we have a new case to solve." Sandra walked from desk to desk, slapping down on each one a buff file filled with photocopied documents, before walking across to the white-board on the wall. The three men hastily started thumbing through the papers.

"This," announced Sandra, as she attached a photo to the top of the board with blu-tack, "is Jenny Mulhain, a 19 year old girl who went out to the pub one evening in 2004 with some friends." She wrote the name across the top of the board in marker. "Jenny said good-bye to her mates at the corner of Winton Road in South Beckendon, where her family lived, and promptly vanished into thin air. There was a pretty exhaustive investigation at the time, since there seemed no motive for her to head off under her own steam – no family rows, no secret boyfriends, nothing like that. In the end, though, all the leads petered out, until last week, when a skeleton turned up in some woods a few miles away. Dental records show it was Miss Mulhain. Oh, and although the head was with the body, it had been severed from it. Clean-cut through the neck vertebrae."

Gerry, Brian and Jack looked up from the files apprehensively. That wasn't something you came across every day, even in the Metropolitan Police's Unsolved Crimes and Open Cases Squad.

"If a young woman disappears and turns up murdered, and there's no evidence it was anyone she knew, you'd normally think, "Sexual predator," " said Jack. "With the head cut off, you think, "Ritualistic, highly deviant sexual predator, with some experience, who we'd better hurry up and catch before he does it again." I mean, you don't just walk out of your front door one morning and start decapitating people for kicks from a cold start."

"Yeah, well, that was what DI Williams from Beckendon CID thought, and why he thought UCOS might be able to help. But with the lapse of time it's impossible to tell whether there was a sexual assault. But the body was wearing what looked like a long, white gown."

"A gown?" said Gerry.

"That's what I said. And before you ask, no there wasn't a toga party going on at the pub. All the friends Jenny was with that could still be traced didn't recognise it as something she had ever worn."

"This is just bizarre," said Brian. "Decapitation and a white gown must be a really unusual signature. Do we know of any other murders before or since with those involved?"

"Well, DI Williams doesn't, and nor do I – but since you raised the point, Brian…"

"Alright, I know the drill," muttered Brian. "Investigate the records for any murder that looks like it might be connected."

"Thank you. Jack, you help Brian do that. You'll see from the file that the original investigation looked into anyone with a record for sexual offences living in the vicinity. Could you also look into whether any of them have been up to any naughty stuff since, and if any of it fits the pattern of this murder?"

"What about you and Gerry?" asked Jack.

"We're going to meet the family."

Winton Road proved to be an undistinguished street, mostly of maisonettes with garages below them, in the depths of a pretty undistinguished South London suburb. Going from the files, Mr and Mrs Mulhain must have been in their early sixties, but they looked ten years older, with the weary eyes of those who know that, sometimes, there is no such thing as "closure". Looking across at the dustbins next to the front door whilst Sandra rang the bell, Gerry noticed the glass recycling box was amply filled with empty gin bottles.

"Jenny was our eldest," said Mrs Mulhain, hesitantly, as she led the way to the living room. "At the time, she was working as a clerk at the local hospital. She'd just started the job. Truth be told, she'd just started life. She was a trusting kid really. A bit naïve."

Gerry and Sandra sat down in chairs next to each other facing the TV set. The Mulhains took the sofa at right angles to them.

"What do you mean by "a bit naïve"?" asked Gerry.

"She was just a typical nineteen year old, I suppose," said Mr Mulhain. "I mean, she tended to take people at face value. She sometimes didn't see the truth under the surface."

"Mr Mulhain," said Sandra, "I know this is a difficult question to be asked, but do you think Jenny might have gone off with someone she knew that evening, after she'd parted company with her friends? Someone who had something going on under their surface that she didn't realise?"

"I don't know about anyone in particular, and she never mentioned anyone like that, but I can believe she might do that, yeah."

"We told the police this at the time," said Mrs Mulhain, "but, of course, it was all really vague, because we couldn't specifically say that she had a…a boyfriend or that we knew anyone she might have gone off with. It was just this gut feeling we had about Jenny."

"Well, we take parents' feelings about that sort of thing seriously," said Gerry. "Do you know anything about Hare's End Woods?"

"That's where they found Jenny, isn't it?" said Mr Mulhain. Gerry nodded. "It's a bit of a dump, really. . . the sort of place where winos and kids smoking dope go. I wouldn't hang around there after dark. But there was a lot of talk on the estate that summer about misbehaviour in Hare's End Woods. Loud noises, funny goings on. If you want the details, Javed Mansour might be able to help. He's been running the Neighbourhood Watch for years."

Mrs Mulhain snorted. "He's been an annoying busybody for years, too. I warn you, Superintendent Pullman, if you give him half a chance, he'll complain to you about everything the police do round here and everything that everyone else does to. Honestly, he's a right pain in the arse."

"Don't worry, Mrs Mulhain," said Sandra. "We have a lot of experience dealing with them at UCOS."

"Well, OK," said Mrs Mulhain, doubtfully. "Look, you have to realise – Jenny disappearing nearly broke this family. My two younger kids still don't like even talking about it. Bob had a nervous breakdown, nearly lost his job, we came close to getting divorced and spent years in marriage counselling. The one thing that kept me going was that there had to be justice for Jenny. Someone had to pay for this. We've spoken to so many policemen over the years. But we just need one of them to actually catch this person."

"So, no pressure, then," said Gerry, as they walked away from the maisonette and along the gangway towards the steps at the front of the block.

"Well, what do you expect from a victim's parents? Of course they want the guy caught. If you don't like the pressure of dealing with that, Gerry, you've spent over thirty years in the wrong job. "

"I know," sighed Gerry. "The problem is, they all want you to find the guy that did it, and then half the time you can't, or you can't prove it, or it turns out he's disappeared to Thailand or died years ago. Let's just hope this isn't one of those."

They walked across the estate to the small parade of shops of which only a Paddy Power and Mansour's Newsagents remained open and unshuttered. Three teenagers were messing around on skateboards on the paved area in front, but they disappeared quickly when they saw the two detectives approaching.

"Sometimes, I wonder why we even bother with the plain clothes," said Sandra.

Javed Mansour turned out to be a fat Asian man in his fifties, with a permanently suspicious air, as though anyone who walked into his shop might start filling their pockets with Mars bars or packets of Benson and Hedges the moment his back was turned. To be fair to him, some of them almost certainly would. A sickly sweet smell of sugar and E-numbers rose from the shelves of cheap sweets adjoining the counter.

"Police? Where were you when I phoned yesterday about those kids, eh? They're a bloody menace on their skateboards! Some of the old ladies are frightened to come down here now in case they get knocked over. They just laugh if you tell them, and no-one does anything about it. I tell you…"

"Mr Mansour," cut in Gerry. "If you have a problem with the level and nature of response of the local police to your anti-social behaviour problem, I suggest you take it up with them at the nearest police station. We're here about the murder of Jenny Mulhain, which I take it you're aware of." He indicated the stack of copies of The Beckendon Bugle on the counter. The headline on the front page screamed: SKELETON IN WOODS WAS MISSING GIRL.

"Well, I…yes, of course. How can I help you?"

"We understand that you're the Neighbourhood Watch Co-ordinator and that you might have information about strange goings-on in Hare's End Woods around the time of Jenny's murder," said Sandra.

"Well, for a start, there's always strange goings-on around there – asylum-seekers sleeping rough, kids going there to get drunk and take drugs…"

"Yeah, we've heard all about that!"

"…but actually, the funny thing that summer was how a lot of that stuff just stopped. I get loads of kids in this shop, and if you listened to their conversations around then a lot of it was, "Are you going down Hare's End?" "No, it's gone all weird, there's dodgy people hanging around there, it's scary." Then you'd get people talking about bright lights there at night, people burning big fires and funny noises, especially if they'd been anywhere near there at night or if they lived on the top floors of Morrison House. It faces the woods, you know."

"Didn't anyone report this to the police at the time?" asked Sandra.

Mansour shrugged. "They did, so the local station would send cars to drive out there and patrol around a bit. They never found anything. Then a couple of days later it would all start up again. But as soon as that Mulhain girl disappeared, it all went quiet for some reason. It was really creepy, to tell you the truth."

"We're going to have to check out whether that was investigated at the time," said Gerry. He thought to himself that there had to be a link between two events as strange as those, happening so close together.

"We will," said Sandra. "Better still, let's go up there and take a look for ourselves. Thank you, Mr Mansour. We'll be in touch if we have any more questions."

"What about those skateboarders, though?" asked Mansour, as they headed towards the door to leave.

"Try telling them it doesn't actually impress girls," called back Gerry.

They drove over to the woods, which lay in a dark, compact mass just off the main road between South Beckendon and Beckendon town centre. They were surrounded by a wooden post-fence, but there looked to be more hole than fence to it these days, and anyway a public footpath clipped across one end, so there was no serious bar to anyone accessing them. Inside the fence was the usual urban woodland – close-growing, gnarled trees that never got thinned out properly, masses of ivy and brambles filling the gaps, a lot of mud, and a plentiful scattering of empty beer cans, old crisp packets, blue plastic bags and faded newspapers. You could easily imagine the anti-social happening in there, but not the truly sinister.

There was a large clearing near the centre of the woods, in which stood their only really distinctive feature – a massive rectangular block of concrete lying on one of its long sides, for all the world as if someone had dropped it into place from the air. It was difficult to see what it was doing there otherwise, as there was no sign of any kind of building nearby. The skeleton had been found buried under some bramble bushes not far from the clearing. That area was still taped-off, and a few disconsolate-looking Scenes of Crime Officers in white protective suits were poking around, under the supervision of a tall, grey-haired man.

Sandra and Gerry walked over, produced their cards and introduced themselves to the man, who proved to be Detective Inspector Williams.

"Good to see you guys aren't letting the grass grow under your feet. I've only really popped over here myself. The search is basically winding down – the SOCOs tell me they've found all that we're likely to here."

"Which is…?" asked Sandra.

"Not a hell of a lot, Ma'am, to be honest. You know about the white gown Jenny had on, which is with the lab in the event they can find any fibres or hair or anything on it. You know about the head being cut off, which suggests whatever happened here probably wasn't your average murder. And that's basically it. No weapon, body mostly long gone, no idea of where this girl went to after her friends left her. Have you got much to add?"

"Well," said Gerry, "everyone seems eager to tell us that there was a lot of weird stuff going on around these woods at the time Jenny went missing."

"Oh, all those tales? Yes, I've heard them too. I reckon every copper who's ever worked round here has. Hare's End Woods have always had a reputation for funny goings on, but we've never been able to find any solid evidence of anything but teenagers sitting around camp fires drinking bottles of cider. Mind you, there is one thing we found. Look at this."

He pulled a plastic evidence bag from his pocket. Inside it was a flat piece of polished green stone, about three inches by two inches, and on it was carved a vaguely human-looking figure, but with a head like an octopus with a mass of tentacles on the face, a bloated body which appeared to be covered with scales, large claws on hands and feet and long, narrow wings sprouting out behind. Neither Gerry nor Sandra could repress an instinctive feeling of loathing at the sight of the being. A small hole drilled through the stone near its top suggested that it might have been worn on a chain or string, perhaps as a necklace.

"The SOCOs have no idea what this is," said DI Williams, "and I'll be damned if I do either, and whatever it is, it gives me the creeps. We found it near where the body was buried, so there might be a connection, but we have no idea what. Obviously, I have to keep it for my investigation, but I'd be happy to e-mail you a photo."

"Please do," said Sandra. "It could be relevant and…" A mobile phone rang out suddenly and irritatingly. "Excuse me."

"Sandra?" It was Brian. "Have you finished down there? Because we think you need to get back and see what we've found as soon as possible."