Disclaimer: I do not own Harry Potter. Not even a little bit.

'Alright' said Hermione, pacing their office. 'Shoot.'

'The post arrived at 10:18 or there about, Hogwarts letter included, and the mother – Mrs. Cooper- brought the letter upstairs to Ethan.' Began Luna, sitting at the desk and apparently absorbed doodling on a sheet of scrap parchment. 'She gave the letter to him, went back downstairs again, and heard or saw nothing unusual until around 12:45, when she went upstairs to tell him lunch was ready, and….'

'Found him dead' finished Hermione.

'Yes.'

'Were they alone in the house?'

'Just the two of them, yes. Father was at work, older sister away at University.'

'Hmm…' murmured Hermione, deep in thought. 'Would she have seen anyone entering the house?'

'Undoubtedly. She couldn't see the door itself, but she had an unrestricted view of the hall and the stairs. She saw nobody.' Luna paused. 'It's worth noting that she never actually discovered the contents of the Hogwarts letter. She is still unaware of the magical community.'

'That is interesting.' remarked Hermione. 'The letter was burned to ashes. Why burn the letter? They had already killed the child, what did they gain from delaying their escape?'

Luna finished her doodle with a flourish. Hermione leaned over, and saw it was a small map of Ethan Cooper's room with all the possible ways in marked and annotated. In the corner was a caricature of Hermione, and something that the witch strongly suspected was a Crumple-Horned Snorkack. 'Your turn' Luna reminded her. 'What have you got?'

Hermione consulted a small blue notepad before answering. 'Time of death 10:23, five minutes after the letter arrived. We have no way of knowing whether Ethan had already read the letter before he was killed, but it is probable he did. Cause of death, one use of the cutting curse – sectumsempra- aimed at the back of the head. It severed right through the brain.'

Luna hissed. 'Nasty.'

'Powerful, too' Hermione nodded. 'Sectumsempra usually only causes severe wounds, rather than actually cutting through the target.'

Luna frowned in thought. 'The back of the head, you say?'

'That's right.'

'And he was facing…?'

'Away from the door, towards the window.'

'So the killer must have come through the door, which means getting past Mrs Cooper, who saw nothing…'

'A disillusionment charm?' suggested Hermione quickly.

'Or they could have simply modified Mrs. Cooper's memory' added Luna.

'True.'

Hermione looked at her notes again. 'The window showed no traces of magic, so they definitely did get through the door. We can presume they killed the child first, and then set fire to his Hogwarts letter, and then left the way they arrived.'

There was a moment of contemplative quiet.

'So…' said Hermione, breaking the silence eventually. 'What we've got is a murder with actually no suspects. We know they were magical, because otherwise they couldn't have got past Mrs. Cooper, and we know it wasn't her because she couldn't cast the curse that killed the victim. That really doesn't narrow things down much.' She sighed. 'Give me a locked room mystery any day.'

'The question is not whom.' Said Luna slowly, in her slightly absent tone of voice. 'The question is why.'

Ω

The door to their office burst open, breaking them out of their thoughts, and Tonks' assistant, Marcus Threft, entered, looking flustered and out of breath.

'The Chief wants you' he said agitatedly. 'There's been another one.'

'Another what?' asked Hermione quickly.

'Another murder. Just like the first.' he said, gesturing anxiously to the door. Luna and Hermione swept past him, striding towards Tonks' office, while he hurried a step or two behind them in an advanced state of worry. They strode into Tonks office to find her waiting for them, reading a file.

'Mabel Latimer, eleven year-old' she said without looking up. 'Murdered in exactly identical circumstances, right down to the burned letter and the curse used.'

There was a long pause.

'Blast.' said Hermione quietly. Then she leapt into action. 'You, Threft, contact Hogwarts and get a list of all the muggle-borns sent letters who have not yet received them' she ordered quickly. Threft paused a moment, and then ducked out of the office with a respectful nod.

Hermione continued, speaking with an almost frantic speed. 'One murder is exactly that – one murder. But two identical ones mean that they've not finished yet. There's nothing linking the two victims, except their acceptance letters, correct?' She aimed this last at Tonks, who nodded.

'As far as we can tell.'

'Then those letters must be what the murderer is focusing on. And we can use that to catch them.'

Luna nodded. 'Predict their actions. Very good.' she said vaguely.

Tonks looked grim. 'This is getting worse by the day.'

Threft hurried in, holding a sheaf of parchment. 'The list of potential students' he announced, holding it out for Hermione. The witches stared at him.

'How on earth did you get it so quickly?' asked Tonks, somewhat disbelievingly. 'Have they invented owls that travel at the speed of light?'

'Well-' began Luna.

'Not really, Luna' said Hermione without looking away from Threft, who began to shift uncomfortably.

'I…have a friend in the admissions section who lent me a copy of the list' he admitted embarrassedly. 'I wanted it for an old friend – a different one – who has an eleven-year old daughter.'

'And who couldn't wait for the letter to arrive.' finished Tonks in annoyance. 'You are lucky I have bigger problems at the moment, Threft, or you'd be facing serious charges for trading and handling classified information. There's a reason that list is secret.'

'There is' confirmed Luna, who was rifling through the sheaf, 'for instance, to stop psychopathic serial killers stealing the relevant part of your list and using it to murder eleven year-olds.' She finished flicking through the parchments and pointed the papers at Threft accusingly. 'The section for the London area is not present. Is it with your friend, or…?' she let the question hang in the air.

Threft swallowed nervously. He was starting to sweat. 'I didn't give the list to anyone. It was in my desk the entire time, I swear.'

'Then' said Hermione grimly 'Someone broke into the ministry to steal it.'

Tonks was beginning to swell, and almost correspondingly, Threft was shrinking back, trying to make himself as small as possible.

'Hang on' said Luna, pointing at Hermione and ignoring Threft, who was now trying to subtly put her between him and Tonks. 'That doesn't work. How could the thief (and, presumably, murderer) know that Threft had stolen the list if he wasn't already in the ministry, and working close enough to pry into Useless here's desk when he wasn't watching?'

Hermione, looking frustrated, waved the comment off. 'Whatever. We can work that out later. The important thing is that we have the list-'

'Not the relevant bits.'

'Damn! Yes, we'll have to contact Hogwarts after all…but in the meantime, I suppose we should look at the new murder.'

Luna nodded, and the two detectives extricated themselves from the confrontation happening the office, leaving Threft with nobody to hide behind. He pressed himself against the wall as Tonks advanced slowly. The pair left, closing the doors behind them, just as the shouting started. They walked in step with each other, and in silence, both lost to their own thoughts.

Serial killers, what fun! Things are starting to move a little quicker now, so I should be able to get a few more chapters out before the wrath of exam season hits me like the proverbial speeding train. Tell me what you think! Write a review! Flame your heart out!