Opening a side door, Mrs Kilpatrick led Kate and Laura out, across one of the playgrounds, through a padlocked gate in the wire perimeter fence, to what resembled a small bungalow, hidden away in a thicket of trees, out of sight of the main school.

‘How does he get out?’ Kate asked.

Mrs Kilpatrick paused before knocking on the weathered door. ‘I don’t understand your question.’

‘I mean, when he wants to go out, to the shops or the cinema or wherever, if the school gates are closed during the day and at night, how does he get in and out of the grounds?’

‘Oh, he has his own private exit.’

Kate narrowed her eyes. ‘Where?’

‘Just round the back of here,’ she said, moving away from the door and skirting across the rough and muddy ground to the rear of the building. ‘There you go,’ she said, pointing.

Beyond Mrs Kilpatrick’s finger was a high brick wall separating the grounds from the main road, but built into the wall was a thick iron gate. A digital keypad flashed on the wall next to the gate.

‘My team weren’t aware of this third exit. We were told there were only two entrances and exits, apart from the main school building itself: the teachers’ car park and the student entrance.’

Mrs Kilpatrick looked bemused. ‘Well, nobody comes or goes from here, only Mr Linus. He’s the only person with the code.’

‘Even so, you should have told us about it. Is there a security camera monitoring this entrance?’

Mrs Kilpatrick suddenly looked concerned. ‘Well, no, but from here you can only get to the wire fence which leads to the playground and main school building. You’d need keys to get through both, but even then, the sports hall is over the other side of the grounds; there’s no direct route to it. If your suspect had come in here, he would have somehow had to make his way through the school building unnoticed and back out the other side. I don’t think that’s very likely.’

Kate fixed her with a serious look. ‘I’ll be the judge of that. I’ll have one of my forensics experts have a look, regardless. There’s mud, so there could be footprints we can use, or possible fingerprints on that keypad.’ Kate turned to Laura. ‘Can you have SSD check this out while I talk to the caretaker?’

Laura nodded and peeled away, pressing the phone to her ear.

‘Anything else I should know about?’ Kate asked the head teacher.

Mrs Kilpatrick lowered her eyes, realising her mistake, and simply shook her head.

Linus still hadn’t opened his door as Kate returned to the step, so she knocked, leaning closer to listen for movement. ‘Are you sure he’s in here? Is it possible he’s somewhere else on the grounds?’

Mrs Kilpatrick moved away. ‘He said he was coming back here. I’ll go and check he’s not somewhere in the school.’

Kate remained where she was, and banged the door again until it eventually opened, and the caretaker, looking every one of his sixty-plus years, and wearing a flat cap pulled low over his eyes, answered.

‘Mr Linus.’ Kate smiled supportively. ‘Can you spare me a few minutes for a chat?’

He nodded, his movements jittery.

‘May I come in?’ Kate asked.

He looked uncertain of an answer, but eventually stood to one side and allowed her in. As she passed, Kate breathed in and understood instantly why his eyes looked so bloodshot, and why he’d been so reluctant to let her in.

Kate found herself in an open-plan cabin, a television and armchair in one corner, a small kitchen cooker, fridge and sink facing the school, and presumably a small bathroom and bedroom beyond the two doors at the back of the room.

‘Keeps the cold out,’ he muttered nervously, as he saw her eyeing the tumbler on the table next to the chair in the corner.

‘None of my business, Mr Linus. I’m sure tonight’s events have come as a great shock to you.’

He rinsed a mug at the kitchen sink, drying it with the edge of his T-shirt. ‘You want a tea or coffee?’ he asked, switching on the kettle.

‘I’ll pass.’ She waited for him to finish fixing his cup of coffee, with more than a generous helping of sugar, and retake his seat before she continued. ‘Earlier this evening, when you started doing your rounds, had you already had a drink? I smelled it on your breath when you returned with the bolt cutters.’

He placed his mug next to the tumbler and lowered his head in shame. ‘I’ve been stone cold sober for seventeen years before today. But after what I saw…’ His words trailed off.

‘So you didn’t have a drink until you fetched the bolt cutters?’

He shook his head. ‘The stupid thing is,’ he lifted the bottle of whisky from the floor, a quarter already gone, ‘this was a present from one of the children at Christmas. It was so sweet that he’d thought of me that I couldn’t refuse it. I meant to give it away, but I guess I forgot and it got put away in a cupboard. I don’t usually keep anything like that near me; to avoid the temptation, like. Now look at me.’

Kate couldn’t help sympathising.

He allowed the bottle to drop from his hands. ‘When you’re in recovery, you’re told to take it one day at a time. But when something as awful as this… I’m sorry. When I saw that body, I-I-I…’

Kate crouched by his feet, and rested her hands on his, surprised at how ice-cold they felt. ‘You don’t need to feel ashamed in front of me. The key is not allowing yourself to become dependent again. Tomorrow is a fresh start.’

When he looked up, his eyes were watering. ‘It’s not right, though… how can something like that happen in a school?’

‘My team will discover what happened, Mr Linus, I assure you of that. Which is why I’m here. I want you to run me through your actions this evening. When did you start locking up?’

He wiped his nose with the back of his rough and wrinkled hand. ‘I start just after six. Most of the teachers have usually packed up and gone by then, especially on a Friday. I went through the gate and across the playground, letting myself in to the school. I stopped to chat to Janice as she was mopping the Year Five classroom—’

‘Wait, who’s Janice?’

‘One of the cleaners. West Indian lady, very friendly.’

‘And she was still there after six? Mrs Kilpatrick said the cleaners are usually gone by then.’

‘They are usually, but it depends what kind of a state the classrooms have been left in. The teachers are supposed to make sure their rooms are tidy, but some aren’t as thorough as others.’

‘So, it wasn’t unusual for Janice to be here?’

‘No.’ The first sign of a smile appeared. ‘I like to think that sometimes she works slower just so we can have a chat when I come round. Silly, really.’

Kate glanced around the room again. A bookcase was full to bursting with a variety of books, but a thick layer of dust clung to the edge of the shelves. She didn’t imagine he had many visitors.

‘How long would you say you were chatting?’ Kate pressed.

‘Maybe ten minutes or so.’

‘And what were you discussing?’

He sighed. ‘Her plans for the weekend, the cold weather – that sort of thing. She’s going to visit her daughter in Nottingham tomorrow. It’s her grandson’s third birthday.’

‘What time did you stop chatting?’

‘I waited until she’d finished her mopping and had put her equipment away, and then I escorted her to the school gates and ensured she was off the premises before continuing to check the classrooms and lock the doors. I remember looking at my watch and it was about quarter to seven when I headed out to check the sports hall. I thought if I hurried, I could be back to watch The One Show, you see?’

‘Did you notice anything strange as you checked the classrooms? You didn’t hear or see anything that struck you as odd?’

‘No.’

‘And you didn’t see anyone lurking around either inside or outside of the school?’

‘No.’

‘What about this week? Has anything struck you as odd – no matter how small – anything at all?’

‘I’m sorry, but no.’

‘Okay, so you headed out to the sports hall at about quarter to seven. What first alarmed you?’

‘It’s funny, really, but I don’t usually approach the sports hall directly. Usually I check that the fence gate is padlocked, and then go on my way. I don’t really know what inspired me to go and check the door to the old building. Maybe it’s all the visitors who’ve been there this week—’

‘Visitors?’ Kate interrupted. ‘What visitors?’

‘The building inspector… oh, what’s his name? Um… Phillips? Is it Mr Phillips? I think that’s his name. Anyway, he’s been by a couple of times and a couple of others in hard hats too. They’re due to start the demolition in a few weeks. You knew that, didn’t you? They’re knocking it down to put in a swimming pool. I still remember when they built it and it was considered new. A lot has changed since then. The world moves on.’

Kate jotted the building inspector’s name in her notepad to follow up on. ‘When was the last time you’d checked the padlock on the sports hall? You said tonight you immediately knew it had been replaced.’

‘Probably last Thursday or Friday. As I said, it isn’t an everyday thing I do.’

‘And when you saw it had changed, what was your first thought?’

‘I thought it was odd. I am responsible for all the locks and keys in the school, but nobody had informed me that the padlock had been changed.’

‘What made you go and look through the window?’

‘God, I wish I hadn’t looked.’

‘But you did, and something drove you to, but what?’

‘I was being nosy. Mrs Kilpatrick, she… she plays her cards close to her chest. I wanted to see what progress they’d made on preparing the building for demolition. I assumed that maybe the building inspector had put on the new padlock, but I wanted to just have a peek inside. That window at the back is the only one that looks in on the hall. It was already dark outside, but there was just about enough light to see inside. I couldn’t understand what that cloth was on the floor, so I leaned in closer, and that’s when I… when I saw the outline.’

‘You know now that what you saw was in fact a resuscitation doll, covered in a tarpaulin?’

He nodded. ‘Bet you think I’m a silly old fool for rushing to get you. But I swear I thought it was a real person beneath the sheet. The news and papers have been so full of pictures of that little girl who is missing that I-I-I… I must have let my imagination run away from me. I thought maybe Daisy hadn’t gone missing like the press were saying and had somehow got into the sports hall, and maybe something bad had happened to her… I don’t know. I watch a lot of those crime dramas on the television.’

‘Are you aware that we discovered what we believe to be the scene of a murder inside the gym?’

He nodded grimly.

‘Mr Linus, I need you to exercise your discretion with that information. We don’t want to cause a panic—’

He grunted and waved away her concern. ‘Who would I tell, eh? Got no family, or friends to write home about. Most of the time I just potter about here, reading and watching the television. It’s a simple life, but easier that way. At least, it was…’

‘Your personal gate, Mr Linus: are you the only person who uses it?’

He nodded.

‘And nobody else knows what the code is?’

‘No, it’s for my private use, not that I use it as much as I’d like.’

‘Is it possible that anyone else could have discovered the code? Is it written down anywhere?’

‘I have it scrawled on a piece of paper in my wallet – memory’s not what it used to be – but my wallet is always on me.’

‘But if someone managed to get hold of your wallet, they’d have the code?’

‘But nobody has.’

‘But if they did?’

‘Well, yes, then they’d have it, but that hasn’t happened. Most of the staff don’t even know the gate is there. The students aren’t allowed this far back and the property shields the gate.’

Kate wasn’t convinced, but SOCO would confirm if there were any foreign prints on the keypad or in the mud soon enough. ‘One final question, Mr Linus: does anyone else have access to the gate leading to the sports hall?’

‘Only the groundsman who tends the lawn over that side.’

‘He has a key to the gate?’

Linus nodded. ‘But only for that gate. He still has to go through the school building to get to the fence.’

Kate scribbled a note and straightened up, handing Linus her business card. ‘If you remember anything else – no matter how trivial – will you give me a call?’

He took the card. ‘You’re not going to tell Mrs Kilpatrick about… about this?’ he asked, eyeing the tumbler.

‘It’s none of my business, but I’d get yourself cleaned up by the morning.’

His tearful eyes thanked her, and she showed herself to the door, pulling it firmly behind her. Closing her eyes, she allowed her other senses to come to the fore. A bird crowed off to the left, and a car passed somewhere off to the right; the bitter breeze scraped at her cheeks, and the damp smell of the mud and decomposing leaves threatened from behind.

Why here? Of all the places to murder a victim, why a school where security is heightened, and the environment itself is a bedrock of morality and order? Whoever they were now hunting was like nobody she’d come across before, and she already sensed it would take all of her know-how to catch whoever it was.