Starving, but no time to think about it; burying ourselves in the library, trying to find the key – any key – to Dad.

What happened, is he alive, could he possibly be? Does Basti know?

Scruff and Bert are right beside me scouring drawers, opening books, checking under chairs, looking for mysterious letters of instructions or crosses on maps, old family records, something, anything. Turning the room upside down and carefully placing everything back. We’re not getting any help from Basti – we have to do this ourselves.

But nothing. Absolutely zero in terms of clues.

‘Operation Desert Tracker has to widen its footprint, troops.’

‘Okay, what’s next?’ Scruff asks.

‘Basti’s polar bear room. His inner sanctum.’

Deep breaths, nods. It’ll be tough. It has to be done.

‘Hang on,’ says Bert, ‘where’s Pin?’

We look around. Not a sign. Groan. Not again. And it’s far too quiet, in terms of Pin-noise. Which is terrifying. He’s not close.

‘Quick!’

Frantically we run through the house – top to bottom – all the rooms we know. More frantically we do it again. Completely nowhere. And no gaps to escape from, anywhere. How can a little boy just . . . vanish? Silently. Is he in a stomach of some sort? Been spirited somewhere else? My blood runs cold as I think of Dinda, how she said we must never disappear on her, like she almost expected it. There’s so much going on here we don’t know about. And the only way out – the scullery window – is well and truly fixed. We scour the house all over again.

‘Hang on, what’s that?’ Scruff whispers.

We’re back in the kitchen, the third time around. There is a tiny wooden door in the far corner, behind an armchair. Child-sized, Pin-sized – and slightly ajar.

Bingo.

Dad’s slingshot with my name on it is whisked from my pocket. Ammunition? Walnuts from a bowl on the table. Stuffed into pockets, as many as I can. Scruff does the same. Takes out his smaller slingshot from his pocket in readiness. Bert goes to the kitchen drawers and finds a breadknife.

‘Ready and armed?’ I whisper.

‘Proceed.’ Bert nods, grim.

Slowly, slowly I push open the door. An almighty creak. We wince. What has Pin found?

A passageway. Dark. We can hardly make it out. We creep reluctantly inside. It’s cobwebby. Narrow. Damp. Dirty yellowy water drips from rounded bricks above us. Urgh, goodness knows what’s in it.

‘Eeek!’ Scruff squeaks, brushing at his shoulder as something – what? – drops onto it. The tunnel leads under the footpath. How can that be? Where does it end? It’s too dark to make out. No torch. Urggh.

The floor slopes – not good. The passage gets narrower – not good either. The air gets chillier like hundreds of ghosts are crammed into this space and screaming silently to be free – definitely not good. My heart feels like it’s leaping out of my chest here. There might be some ancient torture chamber at the end of this, a medieval skull tomb, a pit of snakes, a cage full of lost kids or worse, their skeletons. I want to be anywhere but here and yep, I’m first. Can’t let Scruff know my terror. Can’t let Bert know because she’ll laugh. Don’t scream, keep moving, keep calm.

‘Do we really have to do this?’ my brother moans as if on cue. ‘I’m not sure Pin’s here.’

‘Dad would never forgive us if he is,’ I hiss back.

‘Leave no stone unturned,’ Bert adds, her voice wobbling, ‘come on.’

Pardon? Is my little sister actually working with me for once? Well well. This is a first. I grin my thanks in the gloom, she grins back. Scruff pushes on ahead of us in a strop of bravado. Cobwebs like ghostly curtains cling to our faces, we tear them off. As scared as each other and refusing to admit it, any of us. Pushing on, down, down. Weapons poised.

A feeble light ahead, a room, at last.

‘Pinny Pin!’ Scruff exclaims.

At the saddest, sweetest sight. Our little man. Sitting on an upturned wooden crate, a towel around his neck like a Superman cape and a crooked crown, from the attic no doubt, on his head. In front of an attentive line of moth-eaten china dolls and dusty, ragged clowns and the baby croc in its glass jar and Pin’s trusty teddy, Banjo, who’s now swamped in a yellowing lace Christening gown, a tin hat and a vast array of military badges. Opened in front of him is Dad’s copy of The Jungle Book, the one thing from home I’d managed to pack. And he’s telling the story – pretending to read – in exactly Dad’s voice. Almost word for word because he’s learnt it off by heart. We all have, thanks to Dad.

I drop down to him.

‘Friends, Kicky!’ Pin cries, beaming to see me. ‘I found them in the attic. We’re at school now. Sssh,’ he adds sternly. ‘It’s story time. The most important bit of the day. You know that.’

‘Oh you you you!’ I laugh through glittery tears. All that panic for a line of teddies!

We glance around at a strange curved room. The walls and ceiling are covered in corrugated iron. Cages for children, my foot. All that’s in it are two narrow bunks, a steel table, an old crate and some discarded tins of food and gas masks. Bert tries one on for size, giggling. ‘Where are we?’

‘You are in what is known as an Anderson Shelter, Miss Albertina,’ booms a voice behind us. We shriek.

Charlie Boo.

Looming at the door. With two bright yellow snakes poking curiously and most delicately from his pockets.

‘You have chanced upon the shelter that your uncle would retreat to whenever a bombing raid was imminent. The neighbours tried endlessly to get him to the tube station at the start of the London Blitz, banging on his door and checking up on him, trying to lure him to safety, but he wouldn’t have a bar of it. He just wouldn’t leave the house, to their anguish. Little did they know he was all prepared down here. Quite cosy in fact.’

‘What about the neighbours – were they all right?’ Bert asks.

‘Lucinda next door was never here, thank goodness – she was travelling the length of the country documenting the war effort. She was always terribly worried about Basti but I set her right. She knew he was in good hands. The Bennett-Joneses on the other side, well, they lost everything. Not everyone was as lucky as us.’

‘Why did the Germans target the houses?’ I ask, horrified.

‘To break us, Miss Kick. To kill us. To crush England’s spirit and force us to surrender, but they did not. And this locality was heavily targeted because of the concentration of tube stations in it. This room is where I, also, would go if I happened to be in the vicinity. Along with the prized guests of the moment – Perdita, naturally, and a few others. If there was time. Sometimes there wasn’t. We were lucky. Very lucky. Someone, I think, was watching over us.’

He glowers over Bert, still in her gas mask, breathing heavily.

‘It is not a place where young ladies are meant to be. Young ladies – and gentlemen – who do not know how to follow rules. Some. Rooms. Are strictly. Forbidden. Remember? This being one of them. Come along at once, the lot of you.’

‘But this is my school, Mr Charlie Boo,’ Pin says gravely. ‘It’s story time. These are my friends.’ The little boy pushes the man back firmly towards the sloping passage.

‘I see. What a shame. Because your uncle has kindly asked me to pop into each one of your deprived little desert mouths . . . one of these . . . when you are found.’ On Charlie Boo’s palm are four tiny, white, sugary Perditas.

We gasp.

‘If you’re good. Oh yes. So thank you most fulsomely, Master Phineas. For I will now be indulging my good self, and self only. Four times over in fact. Thank you, indeed.’

One of the sweets heads straight for Charlie Boo’s lips.

‘Friends, it’s holidays, school’s out!’ Pin yells.

We all laugh.

Now. Brother found, sister on side. Everything under control at last.

Back to the task at hand: secret infiltration of Basti’s polar bear room. Priority: urgent.