Perthshire 1929 and the menfolk of the Gilver family have come down, between them, with influenza, bronchitis, pneumonia and pleurisy. Dandy the devoted wife and mother decides it is time to decamp; Dandy the intrepid detective, however, decides to decamp to the scene of a murder she would dearly love to solve.

The family repairs to the Borders town of Moffat, there to drink the sulphurous waters straight from the well and to submit to the galvanic wraps and cold salt rubs of the splendid Laidlaw Hydropathic Hotel.
But all is not well at the Hydro. The Laidlaw family is at war, the guests are an uneasy mix of old faithfuls and giddy upstarts, and the secret of the lady who arrived but never left cannot be kept for long. And what of those drifting shapes in the Turkish bath? Just steam shifting in the air? Probably. But the Hydro was built in the lee of a Gallow Hill, and in this town the dead can be as much trouble as the living...