Betty Bikes London by Jenny French and Katie Wood

I'll probably buy it but I'll tell my daughter that the yellow vest is only for silly sausages.

I used to work in a children's bookshop, and remember when Choose Your Own Adventure came out:

Betty and Grandpa get separated when his old competitive instincts kick in after being passed by Jeremy Vine on a Boris Bike. Vine vanquished, Grandpa is then forced into an additional burst of speed to escape the grasp of The Bill, who rue that the Smart Hat hasn't yet made it off the drawing board, as the number plate would've made it easy to track down such scofflaws.

Flushed with victory, it takes Grandpa a minute to realise that he's left Betty behind. He races back but unfortunately the police have gotten wise and laid a puncture mat down "for his own good." Grandpa tries to explain the situation as he quickly fits his spare, but they've heard it all before. He impatiently endures a lecture and manages to sweet talk them out of a fine, but it's too late – Betty is not where he left her! Nor did she follow him into the speed trap, though other children are weeping next to their little bikes with shredded tyres in a creche of misery.

Grandpa disconsolately pushes his Colnago (an early Christmas present to himself) into the Winter Wonderland for eggnog and a chance to think, if the strangely familiar-looking busker will turn down the volume. He makes the rounds of the vendors, showing them pictures of his cherished Betty. Although he's not a religious man, he sends up a prayer that she's safe and they will soon be reunited.

When Grandpa raced off, Betty was thrilled! Look at him go, passing everyone, including the silly smirking man! As his backpack filled with energy gels and tea spiked with "Grandpa's little helper" (he'd let her taste it - ick) receded into the distance, Betty's tingle of pride turned into butterflies of uncertainty, then a moose of mild anxiety, threatening to roar into a penguin of panic. Grandpa, come back!

When he doesn't, she remembers what her mother taught her: Look for a grownup in a uniform. Then she spies something better - Santa himself.

"I'm an old fool!" Grandpa can't help muttering, loud enough for passers-by to roll their eyes and hug their children closer. "This isn't the Tour. What got into me? Pride? It always goes before a fall." His yellow safety vest seems to mock him.

None of the vendors remember seeing his precious grandchild, but then most of them quickly lose interest when they realise he isn't buying anything. He wanders over to the Giant Observation Wheel and manages to upgrade to a VIP Pod on the spot as the ticket taker recognises him from his glorious racing days. He even lets Grandpa bring his bike into the Pod.

As the giant wheel slowly turns, Grandpa reflects on a life well lived. He has everything an old man could want: wonderful memories; a beautiful grandchild; a new Colnago, even if it is a bit let down by poor braking performance…

His pod reaches the top of the wheel's arc and pauses, as if in reflection itself, swinging in the gentle breeze like a cradle. Somewhere far below Betty wanders alone, without him. If only she was wearing something that made her stand out from the crowd.

Santa offers Betty no real help, only vague tidings of good cheer. This leaves her at a crossroads, literally. If she was older she might scratch her head metaphorically. As it is she has a real itch, so she removes her colourful helmet

just as Grandpa chances to look down at where she's standing. He's remembered that she's wearing what he called her safety hat, but as she's just taken it off, his eyes carry on their sweep of the crowd.

The giant wheel sets him down on the ground again. His gut tells him she must be here. He knows how much she loves Christmas. He spots Santa and pushes his bike over.

"Have you seen my little girl?" he asks the clearly disinterested day-jobbing actor, picture in hand. Santa waves it away and shrugs. "I've seen a lot of kids, Grandpa. They all look the same to me."

Enraged at his flippant attitude and familiar tone – only Betty is allowed to call him Grandpa – Grandpa pulls off Santa's beard and tries to stuff it down his throat. A little French dog appears from nowhere and starts biting Santa's leg. The police arrive on the scene. The chief constable recongnises Grandpa from before, shakes his head, and is in the process of cuffing him when

Betty suddenly appears, still holding her helmet along with a shred of hope that Santa might come through for her after all. She's shocked to find Father Christmas gagging on his beard, shouting obscenities, and kicking a small dog, but even more shocked to see her Grandpapa. She rushes to hug him and he her, but he's wearing funny bracelets attached to each other. Even more horrifying, he looks as if he's been crying! She's never seen her grandpa cry.

They are tears of joy. Even the constable is touched, and after giving Grandpa a stern look (and Grandpa apologises to Santa) he uncuffs him. It looked like the helmet was going to be an important plot element, but it wasn't.

Betty and Grandpa tearfully celebrate their reunion, the constable sighs at his own soft-heartedness, and the owner of the little dog arrives to call him off but in a spontaneous gesture of seasonal generosity gives it to Betty (the dog is a metaphor for London, even though it's French – there was nothing I could do about its nationality). Santa coughs out the last of the hair from his cheap beard and contemplates his own possibly NSFW happy ending thanks to the crumpled notes Grandpa slipped into his pocket when nobody was looking.