The virus was still killing thousands of people in many countries around the world. But in Harper’s state, lockdown had worked—the virus was nearly under control.

The younger kids were going back to Riverlark and in less than two weeks Harper and her friends would be returning too. She couldn’t wait.

In lockdown Harper had been thinking about all the times she’d let Corey stop her from hanging out with Cleo and Ro. And about the library-captain badge, all but forgotten in her pencil case. She couldn’t let anything else ruin year six. There were two terms left to turn it into a brilliant year to match her expectations.

One Sunday afternoon, she had the idea that she wanted to see Riverlark before everyone else went back. She brought Hector, who fitted neatly into the wire mesh basket on the back of her bike.

The river path was so busy with people taking their lockdown walks that Harper went a different way. She’d been riding her bike on the road more because with everything shut down there were hardly any cars; the roads were as empty as if it were midnight. Today they hadn’t passed one single human. Hector growled at pigeons pecking in the gutter, and then at a postbox and an empty tram rattling along.

At school she put her bike in the rack and scooped Hector out.

‘Hector, this is Riverlark,’ she told him. He always looked like he understood, or was trying.

Hector ran ahead. He growled at the noticeboard and ran down to the sandpit. He barked at it before jumping into it and using it as a toilet. Harper laughed and hurried after him to take care of the mess, while Hector sped off in another direction. She stopped abruptly when she saw Mr Glass walking from the office towards the staff car park, and hid behind a paperbark tree. After a few moments, she heard a car door thunk, an engine starting up…the engine fading. He’d gone.

Harper couldn’t see Hector anywhere. She called him softly, in case any other teachers were lurking. A light rain began to fall. Harper took off her glasses, cleaned them on her T-shirt and put them back on, hoping Hector would magically appear.

She walked briskly around the junior building and jogged to the netball court. No Hector. She was getting worried now. She raced around the main building and the art room, across the fake lawn down to the wooden fortress. By now she was shouting his name. There was such a tall fence between school and the river path that Hector couldn’t have got out that way, but she checked all along it for holes in case he’d dug his way out, like Lolly had said the World War One ratters used to do.

The thought hit her that she might not find him. Lolly would be absolutely broken.

She looked up at the swaying branches of the trees that skirted the playground, and heard a noise like voices. There were three ravens on the netball court: one perched on the ring and the others stepping around the base in their careful, mechanical way. Kar-kar-kar-karrr. The ravens sounded like they were warning her. Harper’s fears were dragging her into unreal territory, imagining that the birds had done something to her dog.

Finally—a bark. It seemed to come from inside the toilet block. Harper tried to budge the door but it was locked tight. Another bark: she raced around the corner of the toilet block to a small square area with tall walls on three sides. Her eye was drawn to a long, wide pipe with an open end that pointed into a deep drain. Could Hector fit into that pipe? Lolly had talked about Jack Russells being able to squeeze into small places to chase rats. What if Hector had seen a rat run up the drainpipe and followed it? Her eyes traced the solid pipe up and up to the slate roof; she felt breathless, as if she was trapped inside.

A strange yellow leaf distracted her. It floated slowly past at eye level and landed elegantly in front of her.

Strange, the movement of it.

There was no breeze, yet the leaf lifted up from the ground again. Harper followed as it rose and fell to the ground again. Rose and fell. Rose and fell again. This time it landed down the narrow passage by the side of the library. Students were not allowed down there. She went, cautiously.

The leaf drifted around the bend.

There, the ground was covered in hundreds of identical leaves. Her leaf must be among them. She looked and looked, feeling dizzier, waiting for one of them to rise. The tree they’d fallen from rested some of its branches on the library roof.

Harper was startled again by Hector’s bark and she shouted his name. He appeared in a flash from a door that was slightly ajar: the door at the back of the library. She’d never seen it open, not in all her years at Riverlark.

Hector jumped into her open arms and—wildly wriggling—licked her face. Harper put up with it, she was so relieved. As Hector calmed down, so did Harper. She detected a faint smell of smoke. She sniffed the air. Maybe whoever lived over the fence was having a barbecue. Perhaps that was what she’d smelled that other time in the library.

Now Harper had time to wonder how Hector had got inside. Had this door been left open? Or was there someone in there now who’d let him in?

Hector was panting, his heart pulsing rapidly into her hand. Was he afraid? Harper stepped closer. Inside, the lights were out.

‘Hello?’ she said into the door opening. She could only see a small part of the room. There were no signs of movement. No voice replied. She needed Cleo and Ro with her. Alone, she couldn’t shake the fear.

When had she become so scared of…nothing? It was just the library, where she’d spent a thousand happy times. She was sensible Harper, library captain—in a way, wasn’t it up to her to check that everything was okay?

But the thought of the empty school now filled her with horror.

Hector squirmed free and jumped to the ground. He raced away from the library at full speed. As she looked back once more through the slightly open door, she saw a change of light and then a dark shape, a fraction of movement.

She ran.

When Harper woke at three o’clock that night, she knew something was wrong: she was lying in something cold and wet.

At first she wondered where she was. But this time, she was actually in bed.

She sat up and flung off the covers to find a large dark patch. When she switched on the light, it was red as anything. Her period. She was angry with herself for not wearing a pad just in case. She’d had her period for a while but it had never come at night before. And anyway, each time one cycle was over, she forgot all about the next one.

Harper bundled the sheets into a ball. Seeing how much blood there was, she wanted to call out for her mum and hand the problem over. But Liz was in a place where blood was a sign of something a lot more serious than this. Even if it was a lonely thought, she knew what she had to do. Get cleaned up, find a pad, don’t wake Lolly.

In the duck-egg blue bathroom, she shoved everything into the washing machine, added the washing powder and a lot of stain remover, turned the dial to Cotton and pressed Start. Then she got into the shower. It was different, showering in the middle of the night. As she stood there, she couldn’t help going over what had happened in the library.

She’d seen something.

No, she’d imagined it.

There was something wrong with her.

There was nothing wrong with her—everyone felt strange: it was lockdown.

Afterwards, she googled: What are the symptoms of PMS? The top result said there were 150 symptoms, some common, others rare.

150! Maybe her period explained everything, like why she’d been hearing the sharp ting sound, or waking up at night, and, more recently, sleepwalking. And why she’d been so freaked out at school today.

Liz had told her the obvious symptoms like mood swings and cravings, cramps and sore boobs, but she had no idea about the ones she was reading now. Number 27 was increased sensitivity to light, 28 was increased sensitivity to sound, 32 was ringing in the ears, 39 was blurred vision, 44 was increased sensitivity to odours, 75 was poor decision-making, 83 was brain fog, 96 was anxiety, 104 was paranoia and 105 was fearfulness!

She shut the iPad. That was enough. Everything she’d been worrying about was just her useless period. There was nothing creepy or strange going on.

The badge, too! That was all just in her head.

Harper found a clean T-shirt and a pad. She laid a towel on the mattress, pulled one of the blankets over her, and curled up in a ball. She whispered for Hector to come, but he didn’t. Harper felt silly and alone.

But that night, she slept without waking up out of her bed. And the next day, when the sheets came out fresh and white, and she’d made her bed and changed her pad for another clean one, she felt relief. Now that she knew what it was, she’d be ready for anything strange. She could go back to Riverlark and everything would be fine.