The book, narrated by the author, is claimed to be based on a story heard by him from his grandfather about the real village of Taff's Well, in the old county of Glamorgan, and its neighbouring Garth Hill.

On a Sunday in 1917, during World War I, two English cartographers from the Ordnance Survey, the pompous George Garrad and his junior, Reginald Anson, arrive at the fictional Welsh village of Ffynnon Garw.

Anson is a younger and much-decorated army officer, invalided out with severe shellshock from fighting in France, and is just starting to enjoy life again.

Garrard, despite his assumed air of authority, doesn't really understand the technicalities of the measuring instruments he uses, and delegates Anson to explain.

He concludes that ‘it’s possible – it’s just hard work.’ Garrard and Anson have a tight schedule and have orders from London to leave in the morning, but the villagers try to delay them.

Morgan enlists his current paramour Betty From Cardiff (also known as Miss Elizabeth) to make up to Anson, which she does, initially with great reluctance.

Tommy Twostroke, a miner who owns a motorbike, is enlisted to call out friends and relations in nearby villages, to assist them.

Betty, despite her lady-like airs, is a maid-servant in a large house near Cardiff, who visits Morgan on her weekends off in her employer's chauffeur-driven car.

She recognises and appreciates Anson as a gentleman, compared to the uncouth Morgan (who is also two-timing her with Blod Jones, Johnny's sister.)

On Sunday, in chapel, Rev Jones encourages the villagers to finish the work, as the map makers must leave on the Monday morning train.

In a short epilogue, the author recalls that Mr and Mrs Anson stayed in the village and both taught at the school, after Davies left in a fit of pique.

He mentions that two photographs of the events exist, taken by a local pharmacist with an interest in photography, and that every villager later obtained a copy of the new map showing the mountain with the official height.