‘It’s still close to all the things you love,’ Dan says. ‘But the house has a bedroom for you, and one for the baby. And it’s the perfect neighbourhood for a family.’

He says the last word with a kind of awe. I’ve always taken family for granted, but now I can see the simple magic the word offers. Families can be a puzzle, but they don’t have to rely on blood, or genes. They’re formed by trust and truth and love. And once you’ve found yours, it will always carry you home.

Acknowledgements

The inspiration for this book came from our amazing Border terrier, who visits patients and staff on the cardiac ward of our local hospital, as well as going into universities to help students affected by homesickness and exam stress. Like Bear, she’s not keen on other dogs, but loves people and seems to understand what each person needs, whether it’s licks, games or the chance to rub her tummy! To find out more about therapy and care dogs, visit www.canineconcern.co.uk.

I had the privilege of speaking to some brilliant young people who shared their experiences of living with a brain tumour. Without them, I’d never have known that waffle face is a thing, or that Bob is a common name for tumours. Huge thanks to Belle, Jas, Luke, Mary, Molly and Ruby for your honesty and humour, and to Sarah Watson and her colleagues at The Brain Tumour Charity (www.thebrain tumourcharity.org) for so much help with my research. Any errors that crept in are 100 per cent mine.

I invented an entire proton beam therapy unit in Bristol for this book – the UK’s two specialist centres are actually at The Christie in Manchester (thanks to Thérèse Smith for offering to help with play therapy) and University College Hospital in London.

Huge thanks to the thoughtful, insightful Tracey Sainsbury at www.fertilitycounselling.co.uk for talking me through the practical, ethical and emotional considerations around fertility treatment, and to Sarah Rayner for putting me in touch.

Now to the rest of the ‘pack’ – sending wags and treats to . . .

The following cats, dogs and hamsters, and their human companions: Archimedes, Betsy, Blossom, Bluebell, Charlie, Colin, Dinx, Freya, George, Gideon, Hobnob, Jet, Lily, Liquorice, Mabel, Meg, Mina, Pabu, Poppie, Rory, Sheila, Tag and Thor.

My agent Hellie Ogden (and Lexi) at Janklow & Nesbit, for their puppy-like enthusiasm for my many wild ideas. Also thank you to Ma’suma Amiri, Kirsty Gordon, Ellis Hazelgrove, Allison Hunter, Zoe Nelson and Emma Winter.

My editor Sam Humphreys (and Lux, aka Big Dog) for sniffing out the right direction for the book, and always urging me to dig deeper. Also, thanks to Becca Bryant, Elle Gibbons, Alice Gray, Charlotte Wright, Hannah Corbett and Rosie Wilson at Pan Macmillan, and Mandy Greenfield for copy editing so, um, doggedly.

Big thank-you licks to the wonderful guardians of Stanley, Rosa and Molly. And, of course, to the person I’m lucky enough to share Vesper with . . .