Author's note: This takes place between seasons 8 and 9. Spoilers for season 8.

'What have you found?' asked Boyd.

It was team briefing and, as usual, the others let Eve go first,

'My initial analysis supports your theory that we have a previously undiscovered serial killer at work, Boyd,' said Eve, 'All of the victims died of dehydration and the crime scene evidence suggests that they all died where they were found.'

'So why didn't they leave?' asked Spence.

'I think that they were trapped there,' said Eve, slightly hesitantly, 'These nine had marks on their hands which correspond to marks on the doors where they were found and these three had been kicking at the walls.'

As she spoke, Eve pointed to the relevant pictures on the board.

'So, the killer locked them in and left them to die then came back later and unlocked the door?' asked Boyd.

'I think so, yes,' replied Eve.

'Always couples?' asked Kat.

'As far as we know,' replied Eve, 'We've only identified six of the victims so far but they were couples and the other victims are all male and female pairs.'

'All right. Kat, start looking for missing couples from the relevant periods. Eve, do we know when they died?'

'As far as I can tell, this couple, May and Andrew Evans, were the first in nineteen ninety-two. Followed by John and Susan Robinson in nineteen ninety-four, this unidentified couple in nineteen ninety-six...'

As Eve continued, it became clear that the killer was striking once every two years and that he was due to kill again this year. Boyd waiting until Eve had finished then turned to Grace, saying,

'What are we looking for?'

'It's an unusual psycopathy...'

'Come on, Grace, give me something to go on,' said Boyd, impatiently.

'All right but you understand that this won't be very accurate?'

'Yes, yes, whatever. Just get on with it!'

Giving Boyd a level stare, Grace said,

'It's almost certainly a man working alone. He has trouble forming relationships, particularly with women. He may have been locked in a room or a cupboard for long periods of time as a child.'

'You're sure it's one man?' asked Boyd.

'I think so, yes. The method of killing suggests a need to overpower and control the victims himself. Having a partner would tarnish that.'

'Is it sexual?' asked Spence.

'It's hard to say,' said Grace, 'Is there any evidence of food or water being brought to any of the victims, Eve?'

'None.'

'Then it's probably not sexual though there may be a sexual element to it.'

'Very helpful,' said Boyd sardonically.

'I'm sorry, Boyd, but I haven't had time to read the files yet.'

Grace sounded irritated and Boyd backed down, turning to Spence and saying,

'We start at the beginning, with the murder of May and Andrew Evans. When were they reported missing?'

'On the eighth of February nineteen ninety-two, by their son Jason. He came home from school on the seventh, which was a Friday, and found his mother out. There was a note on the table, saying that his parents were going out for the evening and to make his own tea. This was normal for a Friday so Jason made his tea, did his homework and watched television then went to bed. When he woke the next morning and realised that they hadn't come home, he called the police.'

'What did the police do?'

'Initially nothing. Just told Jason not to worry. Reading between the lines, it's clear that they thought that May and Andrew Evans would turn up, hungover and embarrassed by all the fuss.'

'But they didn't?'

'No, Jason kept ringing the police and on the morning of February tenth, he was joined by Andrew Evans' employer, a Paul Jenkins, who was adamant that whatever Andrew might have done at the weekend, he would have been there for work on Monday. Apparently, Andrew Evans had never missed a day's work in eighteen years. At which point the police started making inquiries. However, they didn't have any success and it wasn't until a year later that their bodies were found in the basement of a disused block of flats.'

'And the police had no luck tracing their movements on the Friday night that they disappeared?' asked Grace.

'None. They usually went to a pub or club but no one remembered seeing them at any of their usual haunts.'

'So either they went somewhere different or they didn't get that far,' said Boyd.

'How old was Jason Evans at the time of his parents disappearance?' asked Grace.

'...Born tenth January nineteen eighty, so he was twelve.'

'Was he an only child?'

'Yes.'

'Poor boy. Do we know what happened to him?'

'Went to live with an aunt in Peckham.'

'See if you can track him down,' said Boyd, 'We need to know if he remembers anything else from the time of the murder.'

'Yes, Sir.'

'When it became a murder inquiry, who did the murder squad like for it?'

'A Frank Buskin, Sir,' replied Kat, 'He and Andrew had had a fight a few days before but he had an alibi and there was no evidence linking him to the crime scene.'

'Anyone else in the frame?'

'The police looked at Ted Jenkins, Paul Jenkins brother, because he'd had an affair with May Evans, but the affair had been over for some time before the two disappeared and there was no evidence that Andrew Evans ever found out about it,' said Spence.

'Anyone else?'

'May Evans had had an argument with a friend a few days before but the woman involved, a Rachel Blackwater, was ruled out because the officers didn't think that she was physically capable of carrying out the crime.'

'Why?' asked Boyd, 'Was she disabled?'

'No, just very small. The officer who interviewed her estimated her height as under five foot and she was slightly built too.'

'That doesn't seem an adequate reason for ruling her out. After all, the bodies weren't moved, were they, Eve?'

'No.'

'And there was no sign on the bodies that they'd been restrained or knocked out and then brought there?'

'No, though we can't rule out something like chloroform. The bodies were all found at least two months after death so the internal organs didn't yield any useful information.'

'Carrying unconscious bodies is very hard work, not to mention conspicuous so it's far more likely that the killer got them to walk there under their own steam. So the killer needed cunning not strength. Find out everything you can about Rachel Blackwater,' said Boyd.

'You sure?' asked Spence, 'I thought we were looking for a man?'

'We probably are,' agreed Boyd, 'It's just...imagine you're out for the night with your partner and someone you know slightly tries to get you to go somewhere remote with them...'

'Okay...' said Spence.

'Who are you more likely to go with? Someone who looks like me or someone who looks like Grace?'

'Grace, definitely,' said Spence, grinning, 'I'd be very suspicious if you asked me to go somewhere remote with you, Sir.'

Everyone chuckled and Boyd said,

'Precisely. Grace?'

'Statistically, the killer is much more likely to be a man...but it's not impossible that it's a woman. Let me look at the files and get back to you.'

'Right. Let's get on with it,' said Boyd.

The team got down to work.