Clovelly, 1799. The village falls down the cliff in one cobbled street, so steep that everything it eats and burns and sells goes up and down on sledges.

In December the herring boats come in at dawn, and the old people say that on wild nights the drowned come up the street and knock on the doors of the men who owe them.

Three years ago the surveyor Rhys Pryce fell from the cliffs at Hartland. His daughter Angharad has finished every map he left unfinished but one. She has come to Clovelly because of a single line in his last field-book, written on the only Sunday he ever worked: Rode to Clovelly... Not mine.

On her first night a young clerk asks her to meet him at the quay steps at ten. He never comes. At dawn he is found on the steps, ten yards above the place where she waited for him, with his skull broken, and buttoned inside his coat is a copy of the last map her father ever worked on, with a line pencilled across it in another hand.

The village says he slipped on the cobbles in the dark, and that somebody heard knocking. Angharad knows where the pencil line goes. It goes to the place where her father died.

The fifth and final Field-Book Mystery, following Where the Foxgloves Grow, The Harvest Jug, The Bounds and Wassail Night: a Georgian mystery of herring, sledges and forged signatures, in which the question under all five books is answered at last, by a measurement.