Charlie Bone and the Blue Boa. Jenny Nimmo

she hadn’t told Charlie about the attics. He was inclined to rush into things without thinking them through. But she felt she had no choice but to follow.

      They crept up one staircase after another. Once they bumped into Dr Saltweather, who interrupted his humming to ask where they were going. ‘We’ve been sent to get books from the library,’ said Charlie. And Dr Saltweather waved them on, although they were nowhere near the library. But Dr Saltweather was oblivious to everything but his precious music.

      They ran along dark passages and through empty, creaking rooms and, as they drew near to the west wing of the building, Emma became increasingly nervous. She still had nightmares about the time when her only escape was to become a bird and fly.

      Memory, or instinct, led her to the cell-like room where Manfred Bloor had once imprisoned her. Light from a tiny window showed dark walls patched with green slime, a narrow bed covered in filthy blankets and black, broken floorboards.

      ‘What an awful place,’ Charlie murmured.

      ‘Manfred locked me in,’ said Emma. ‘But then someone turned the key on the other side, and the door opened. I rushed to see who it was but there was no one there. Manfred caught me and brought me back, but – and this is the strange part – he said to someone, “Any more trouble and you won’t get jam for a week.” That’s why I thought it might be Mr Boldova’s brother, Ollie. Because he liked jam.’

      ‘Perhaps he’s been locked in some other gruesome room like this one.’ As Charlie turned to the door it suddenly slammed shut. Charlie lifted the latch and pulled. Nothing happened. The door appeared to have jammed. ‘Must have been a draught,’ muttered Charlie.

      ‘There isn’t any draught,’ said Emma.

      ‘But what else could it have been? No one came in. We’d have seen them.’

      ‘Maybe they were invisible.’

      ‘Hey!’ called Charlie. ‘Is anyone there?’

      No reply.

      ‘What on earth are we going to do?’ cried Emma. She looked at her watch. ‘We’ve only got twenty minutes.’

      ‘This is stupid.’ Charlie rattled the door while Emma pulled the latch.

      ‘It must be Ollie,’ said Emma. ‘Ollie! Ollie Sparks, are you there?’

      Silence.

      ‘Ollie, we’ve come to help,’ Charlie explained. ‘If you’re there open this door, please!’

      Emma and Charlie waited. There was a soft creak. A key turned in the lock. Charlie pulled the door and it swung inwards. There was no one in the passage outside.

      The two children stepped out. They squinted down the shadowy passage, searching for a door, a recess, any place where someone could be hiding. Emma’s foot touched an empty jar and it rolled away, filling the passage with a loud rumble. When the jar finally came to rest, faint footfalls could be heard receding into the distance.

      ‘He’s running away,’ Emma whispered.

      They chased the footfalls down the passage, up a rickety set of steps and into a long room with a narrow skylight. The floor was littered with empty jam jars and comic books. At the far end of the room there was a bed with a clean-looking pillow and a patchwork cover. An oil lamp sat on a small bedside table and a huge cupboard stood just inside the door. There was nothing else in the room except a spindly chair and a battered desk that had been placed beneath the skylight.

      ‘Ollie,’ Emma said softly. ‘Ollie Sparks, are you here?’

      ‘What if I am?’ said a rather mournful voice.

      ‘Why can’t we see you?’ asked Charlie.

      There was a pause before the voice replied, ‘Cos I’m invisible, aren’t I?’

      ‘What happened to you?’ asked Emma.

      ‘The blue boa got me.’

      ‘Boa?’ said Charlie and Emma.

      ‘Snake,’ went on the mournful voice. ‘Awful thing. I saw it, see. No one’s meant to see it. It’s a secret. A secret weapon.’ There was a croaky laugh. ‘Once I’d seen it, they weren’t going to let me tell about it, so they brought me back here, and it – well, I was like a guinea pig – they let the boa squeeze me, only I didn’t die, I just got invisible.’

      ‘Hell!’ gasped Charlie.

      ‘It didn’t get all of me.’ A breathless sort of giggle shivered on the air. ‘It missed my big toe.’

      In horrified fascination Charlie’s eyes were drawn towards the floor. Emma couldn’t help screaming. She had already seen it: a small pink blob, lying just a few steps away from them.

      ‘Sorry,’ said the voice. ‘It used to have a bit of sock and shoe on it, but the shoe got too small, and the sock wore out. A toe’s a bit disgusting on its own, isn’t it?’

      ‘Not at all,’ said Charlie cheerfully.

      ‘They tried to get all of me back,’ said the voice. ‘They made me drink revolting potions, and threw smelly liquid over me, and once they covered my bed in spiderwebs while I was asleep.’

      ‘That is so gruesome,’ said Emma.

      Charlie said, ‘Ollie, why don’t you escape? The door’s not locked. You could easily run away. No one would see you.’

      ‘You try it.’ The voice sounded very aggrieved. ‘I came out once. People walked into me, knocked me down – some of them screamed. I couldn’t get out of the main doors, no one can. I didn’t feel safe, so I came back here.’

      ‘It must be so horrible, all alone,’ said Emma. ‘What do you eat?’ She was actually wondering how Ollie ate, but was too polite to ask.

      ‘The food’s mostly disgusting, but Manfred gives me nice jam. I suppose he does it to keep me quiet. And, in case you’re wondering, I eat just like anyone else. Only you can’t see the food once it’s inside me.’

      Emma hoped Ollie couldn’t see her blush.

      Charlie had an idea. ‘If you come down to the dining hall at suppertime, we’d all be sitting still. No one would bump into you, and I could make room for you between me and my friend, Fidelio. The food’s not so bad on the first day of term.’

      Silence. Perhaps Ollie was thinking.

      Emma remembered the most important thing of all. ‘Ollie, your brother’s here,’ she said. ‘He’s come to look for you.’

      ‘What? Samuel? I can’t believe it. Wow!’ Suddenly the pink toe jumped into the air and there was a small thud as two feet landed back on the floor.

      ‘So, if you come down to supper, you can see him,’ said Charlie.

      ‘Yes. Oh, yes . . .’ A pause. ‘But I won’t know the time. I haven’t got a watch.’

      Charlie took off his watch and held it out. ‘You can borrow this.’

      It was disturbing to see a watch gradually disappear into thin air.

      ‘Don’t worry, it’ll come back when I take it off. Everything I wear becomes invisible,’ Ollie explained. ‘Everything I eat or hold or put on.’

      Emma glanced at her own watch and cried, ‘We’ve only got five minutes. We’ll never make it.’

      She dashed out of the room and down the steps while Charlie followed, calling, ‘Sorry, Ollie. Got to get back to class. Hope to see – er – hear you later!’

      Emma and Charlie tore down the empty passages, often taking the wrong turn, or the wrong staircase, but ending up, at last, on the landing above the entrance hall. Their relief was short-lived. Approaching them from the other side of the landing was Dr Bloor.

      The