It is June 1916, four weeks before the opening day of the disastrous Battle of the Somme. Hardcastle is sent to Kingston-upon-Thames to investigate the murder of Colonel Sir Adrian Rivers, a retired and distinguished soldier. The colonel's second wife, Muriel, seems neither distressed by the murders, nor able to assist in the investigation.

It is up to the dogged Hardcastle, aided by DS Charles Marriott, to question an array of characters and narrowly avoid being killed in a Zeppelin raid before the killer is eventually unmasked.