Edwin Scott has just qualified from medical school, and finds himself on the house at a small hospital in Hertfordshire as house physician to Dr Peter Middleton. Initially he feels out of his depth, but, after coping with medical emergencies, such as hypoglycaemic coma, myocardial infarction, meningitis and bleeding duodenal ulcer, he gains confidence. Just when he is beginning to enjoy his work and leisure, the murders begin. Is the killer an outsider, or is he one of the residents of St Peter's Hospital?