Douglas Sewell is shocked to watch his friend John Waterhouse dying in agony. The medical certificate cites the cause of death as gastric ulcers, however the victim's estranged brother Cyril demands that the body be exhumed - suspecting murder. Arsenic poisoning is the verdict and Sewell has to use his knowledge of the characters involved and assessment of possible motives to discover the murderer's identity. The answer is surprising.