One-time doctor turned writer Clio Marsh joins a survival training course based on the Norfolk Broads as part of the research into a new novel – strictly as an observer, she thinks.

 

But course directors, Hollis and Chase have other ideas, and Clio is soon immersed in a punishing boot-camp regime for which she is sorely unprepared.  Most of her fellow trainees fare little better, and within days more than one has succumbed to a mysterious illness whose symptoms closely resemble the ‘marsh fever’ talked of in ominous tones by the locals of Graveleigh, an isolated village at the water’s edge.