Uncovering the mystery of her mother's disappearance as a child: Laura Cumming, prize-winning author and art critic, takes a closer look at her family story.

In the autumn of 1929, a small child was kidnapped from a Lincolnshire beach. Five agonising days went by before she was found in a nearby village. The child remembered nothing of these events and nobody ever spoke of them at home. It was another fifty years before she even learned of the kidnap.

The girl became an artist and had a daughter, art writer Laura Cumming. Cumming grew up enthralled by her mother's strange tales of life in a seaside hamlet of the 1930s, and of the secrets and lies perpetuated by a whole community. So many puzzles remained to be solved. Cumming began with a few criss-crossing lives in this fraction of English coast - the postman, the grocer, the elusive baker - but soon her search spread right out across the globe as she discovered just how many lives were affected by what happened that day on the beach - including her own.

On Chapel Sands is a book of mystery and memoir. Two narratives run through it: the mother's childhood tale; and Cumming's own pursuit of the truth. Humble objects light up the story: a pie dish, a carved box, an old Vick's jar. Letters, tickets, recipe books, even the particular slant of a copperplate hand give vital clues. And pictures of all kinds, from paintings to photographs, open up like doors to the truth. Above all, Cumming discovers how to look more closely at the family album - with its curious gaps and missing persons - finding crucial answers, captured in plain sight at the click of a shutter.