One touch of lunacy makes the whole world kin,” someone says in A Fine Summer Knight, providing a smart summary of the book’s main concern. It’s a novel about kinship the sometimes painful experience of accepting one’s own family, warts and all, and the kinship that can evolve between people from widely disparate backgrounds through shared experiences. And it is about a form of lunacy: obsession.

Main character Grace (known within her family as Auntie) is a lonely child who feels unappreciated and out of place. An accidental glimpse through a telescope of a ghostly knight in armour intrigues and obsesses her. She is driven to discover more even if it means straying beyond the boundaries set for her into forbidden territory.

Grace’s parents are fanatical about machines: the garage and garden of their council estate home are crowded with all manner of arcane treasures a cake mill, stationary engines, a corn-crusher anniversary presents to each other. Older brother Frank and his friend Salvo are obsessed with the restoration of a 1947 Fordson coal lorry, which has been blocking the driveway for years. To complete its authentic restoration they need a wheeling machine, with which to fashion mud-guards.

Here’s where the plots so neatly combine. During her quest to find her knight in shining armour, Grace spots a wheeling machine in the grounds of a big house. This belongs to a well-to-do family, some of whose members have an obsession of their own: the re-enactment of 14th century battles complete with full armour and weaponry.

The tight plot that relies so frankly on coincidence allows space for an exploration of modern childhood. Grace is trapped on her estate, forbidden to stray because her family fear the “nutters” that they think roam the streets. But Dizzy, the “posh” girl from the big house on the hill, is similarly trapped by a snobbish mother who won’t allow her to mix with the local children.

Jan Mark is excellent on detail and atmosphere: the evocation of a decaying stone angel in a graveyard, the flat view through a telescope, the sounds a house makes when you are lying awake in it, all plainly and precisely evoked. Her off-beat characters, dreadlocked trainee plumber Salvo, for instance, are warmly portrayed. And the change in Grace herself, as she makes friends and proves her worth to her family by being the one to save the day, is moving and satisfying.

The early chapters are clogged with detail about machinery and vehicle restoration though the latter is surprisingly interesting. But once Grace has glimpsed her knight the pace quickens into an exciting and thought-provoking read.

There is a shamelessly happy ending as the final chapter brilliantly conveys the glorious mayhem of a re-enacted battle at a steam rally. Two clankingly raucous obsessions combine and the two families to which they are attached are made kin.