The big wheelie bin smelled of banana skins and yesterday’s fish curry, but Ada Lovelake was up to her elbows in it.

“Stay on target,” she said, to nobody in particular. “Almost... there.”

Her fingers closed on something soft and slightly slimy, and she lifted it aloft. “All hail, BlueLoo!”

BlueLoo was a stuffed rabbit who had once actually been blue, once had two ears, and once smelled of nothing much worse than dog. These days it would be quicker to list the things he didn’t smell of. One ear was long gone. The other hung by a thread. His left eye was a broken button. His right eye, a sequin.

The little rabbit was ten years old, same as Ada. Mum and Dad were surprised he hadn’t grown out of her yet. So was she, but she didn’t want to leave him before he was completely ready. And anyway, he was perfect.

She wiped him on her jumper, which didn’t improve either of them, and marched back to the car, where her father had suddenly become very busy with a big cardboard box.

“Dad,” said Ada.

“Hmm,” said Dad, to the box.

“You said you’d packed BlueLoo.”

“Did I?” Dad opened the box and peered inside, as if it might offer him an escape route. “Oh yes, I’m sure I did pack him somewhere. Is there a problem?”

“He was in the bin.”

“He was?” Dad closed the box and lifted it into the boot, keeping his eyes on anything that wasn’t Ada. “Bins, eh? Like black holes in space. Things get sucked in. You’d be amazed.”

“You’d have to lift the lid,” said Ada. “Put BlueLoo in. Close the lid again.”

“That’s the universe for you,” said Dad. “Mysteries everywhere.”

Mum came down the path with the last bag, looked at the bedraggled rabbit in Ada’s hand, then at Dad, and made no comment. Instead she reached down and gently tucked BlueLoo’s stuffing back in through one of his bigger rips. “Come on, then,” she said. “It’s a long way to Grandad’s house.”

From inside the car came a sharp, joyful yip. Millie had spotted BlueLoo. Her whole back end was going wild, her tail whipping across the car window like a furry windscreen wiper.

Ada climbed in and let Millie take BlueLoo, very gently, as she always did.

With everyone aboard, Mum started the car, and was about to drive away when the postwoman walked up the pavement, waving a letter. Mum wound down her window.

“Got one for Jessica Lovelake?”

“That’s me, thanks,” said Mum, and took the envelope.

Ada craned forward. The address on the front looked as if it had been written by a pigeon dancing across the paper with pencils tied to its feet, which could only mean one thing.

“It’s from Grandad!” she said.

Mum opened the envelope with a sigh, and took out a card. The front showed a crowd of little blue flowers, painted in watercolours. Ada counted five round petals on each, with a blob of yellow in the middle.

“My birthday card from Grandad,” said Mum. “Precisely one month late. Again.”

“Like clockwork,” Dad agreed.

“He never got it wrong before my mum died,” said Mum. “Not once.”

Mum read it quickly and passed it over her shoulder to Ada, and started the car engine. Inside, courtesy of more dancing pigeons, it said:

Happy birthday to my unforgettable daughter.

Can’t wait to have you living at home again!

Love,

Dad xxx

Ada read it three times.

The car had gone about twenty yards when somebody shouted her name. Ada twisted round. A small girl with loads of dark hair, none of it brushed, had dashed out of a neighbouring house and was sprinting up the pavement in her bare feet.

“It’s Bug!” said Ada. “Stop the car!”

Mum stopped the car. Grace Hopper, who had been Bug since the first day of school and would still be Bug when she was ninety, arrived at Ada’s open window out of breath.

“One more Bug-hug!” she demanded. She leaned in through the window and squeezed Ada fiercely. “Write to me,” she said into Ada’s hair. “Proper letters. With everything in.”

“Everything,” Ada agreed.

Then the car was pulling away again, and Ada turned to look out the back window.

Bug stood in the road, waving. Beyond her, their house – their old house, Ada realised – was getting smaller. The house looked wrong without curtains. Surprised, somehow.

She watched them both until the corner at the end of their road – their old road – took them away.

“All right back there?” said Dad.

“Yes,” said Ada. It was mostly true.

* * *

It was a long drive. Long enough for the towns to turn into hedges and fields, then back into towns, then into hedges and fields again.

Ada leaned on Millie and watched them come and go, and after a while the grown-ups in the front began to talk in the low, careful voices they used when they thought she was asleep.

She closed her eyes, let her head loll against the window, then kept very still, listening.

“...and if it’s too much,” Mum was saying, almost too quiet to hear. “If it’s more than we can manage...”

“Then we’ll work it out,” said Dad. “We always work it out.”

“You heard him on the phone last week. Asking when my mum was coming home...” A pause. “He’s getting worse.”

For half a minute, all Ada heard was the road passing under the wheels.

“We’ll work it out,” said Dad again, which Ada noticed was not the same as saying it wasn’t true.

She kept her eyes shut and her hand on Millie’s back, and in her mind listed the new things she had learned.

Fact 1: Grandad is more confused than ever, and thinks Granny Pat is coming home.

Fact 2: Mum is worried.

Fact 3: Dad is too, but doesn’t want to admit it.

She didn’t understand the details, not yet. But not-yet was Ada’s favourite kind of understanding. Not-yet meant there was work to do.

Before long, she wasn’t pretending to be asleep any more.

* * *

When Ada woke, Grandad’s house had already started filling the sky in front of the car.

The long driveway sloped upwards, so the house arrived in instalments. A huddle of chimneys first, then a steep dark roof, then a second roof at a different angle to the first, then walls.

The walls didn’t match either. One end was grey stone, the other a brick so dark it was nearly black, and in between the house did whatever it liked, as if it had been built by several builders who refused to talk to each other.

It was very big. Too big for five grandads, she thought. Let alone just one. Beyond the house, a garden, then a little field, then some woods, which carried on up the hill until the hill ran out. Ada marvelled.

“I can’t believe this is all Grandad’s,” she said.

“Eden Wood has grown so much since we saw it last,” said Mum. “That’s good.”

Grandad was waiting for them in a battered armchair outside the front door. If you can call snoring waiting.

Mum beeped the horn lightly and he woke with a jerk.

He seemed small next to the big front door, in a cardigan the colour of weak tea. When he saw them his face lit up like this was the best thing that had happened to him in ages.

Ada was out of the car before it had even properly stopped.

“Grandad!” she yelled as she ran. She managed to slow down just enough not to bowl him over.

“Well,” said Grandad, holding her by the shoulders and beaming down at her. “Well, well. Look at you. Look at you, young lady.” He turned to call over his shoulder into the house. “Patricia, they’re here! Patricia, come and see. The girl’s here, the girl’s –”

He stopped.

“The girl’s here,” he said again, more quietly. The hands on Ada’s shoulders went still. His eyes foggy on the inside.

“It’s Ada, Grandad,” she said.

“Ada,” he said. And then: “Ada! Of course it is. There you are.” He pulled her into his cardigan, which smelled of pipe smoke and toast. She breathed him in happily.

Then the hands on her shoulders tightened, just a little.

Over the top of her head, Grandad was looking at the driveway. At the same old car with its doors hanging open. At Mum standing beside it, holding her own elbows. At Dad halfway up the path with a box. At all of them, arriving.

“You’ve come,” he said slowly. “You’ve all come. Again.”

He bent down, joint by creaky joint, until his face was level with Ada’s. His eyes weren’t foggy now. They were wide with excitement, as if he’d just been told an incredible secret and could barely keep it in.

“I remember! I was going to show you all, last time. I had everything ready. They’re still here. In the house somewhere. I know they are.”

“What are, Grandad?”

“My robots, Ada! The first one, not too bright. The second, too bright by half!” Grandad laughed at the memory. “And the others...”

The laugh trailed off. He squinted and tilted his head, the way Millie did when she heard a sound nobody else could hear. Then he took his hands from Ada’s shoulders, turned them over, and studied his palms, as if the rest might be written on them.

“Help me find them again, Ada,” he said, softly. “Find them, and we’ll show your mother. She never got to see them.” He looked up from his hands and found her eyes. “Please?”

Ada stood exactly where she was. For once in her life, she could not think of a single thing to say.

It was Dad who answered. He had reached the step by now, and he set his box down on it.

“Robots, eh?” he said cheerfully. “Brilliant. Let’s see about a cup of tea first, shall we, James?”

Mum had stayed put, down by the car. Now she came up the path fast, brisk all at once, like a switch had flicked on inside her.

“Hello, Dad.” She kissed his cheek quickly and took his arm in both hands, already turning him towards the door. “Let’s get you inside before you catch cold. And you can have that cuppa.”

Grandad went where he was steered. But at the door he paused and looked back at Ada, and for a heartbeat she thought he might say it again. Instead, she watched his shoulders sag, and his head dip. Then he turned and let Mum walk him inside.

Ada stayed on the driveway with Millie.

Grandad had asked her for help. Whatever anyone said about it later – nobody said anything about it later – and however confused Grandad now was at times – very – Ada knew that he’d meant it.

Grandad had asked her for help, and she was going to give it. She’d do her best to find those robots. But where to begin? Perhaps the house would give her a clue.

She looked up at it. It was even bigger from underneath. So she did what she always did with things that were too big: she found smaller things in them to count.

Windows, this time. Top to bottom, then left to right. She got to twenty-four, and that wasn’t even counting the windows on the older part of the house, where thick ivy had climbed all the way to the roof, and some of the windows were now more leaf than glass.

Twenty-four windows, two roofs, and somewhere behind them all: robots. Real ones, if Grandad could be believed.

Ada had already decided that he could.

Her eyes narrowed. This house would require extensive investigation! She would begin immediately.

Or possibly after dinner.

Immediately after dinner.