The novel is set in
Galloway, a part of
Scotland popular with artists and
recreational fishermen. Sandy Campbell is a talented painter, but also a notoriously quarrelsome drunkard. When he is found dead in a stream, with a still-wet half-finished painting on the bank above, it is assumed that he fell in accidentally, fracturing his skull.
Lord Peter Wimsey, who is in the region on a fishing holiday, suspects murder when he realises that something is missing from the scene which makes it likely that another artist painted the picture. Sayers includes a parenthetical note at this point: "Here Lord Peter Wimsey told the Sergeant what he was looking for and why, but as the intelligent reader will readily supply these details for himself, they are omitted from this page." A local doctor believes that the degree of
rigor mortis suggests that Campbell died during the previous night. Whoever killed Campbell also executed the painting in Campbell's distinctive style, to contrive the appearance of an accident. Six talented artists in the area have had recent public brawls with Campbell: Farren, Strachan, Gowan, Graham, Waters, and Ferguson. One of the six is the criminal, and five are
red herrings. All the suspects behave suspiciously: some leave the district without explanation, others give obviously inaccurate statements or conceal facts. Wimsey investigates, with some assistance from his friend in London,
Charles Parker. The task of identifying the culprit is made more difficult because of the complexities of the local train timetables, the easy availability of bicycles, and the resultant opportunities for the murderer to evade notice. All six suspects are eventually traced and give statements in which they deny killing Campbell, but none are entirely satisfactory. The
Procurator Fiscal, the
Chief Constable and the investigating police officers meet with Wimsey to review the evidence. The police put forward several theories, implicating all of the suspects either as killer or as
accessory. Asked for his opinion, Wimsey finally reveals that the true killer was in fact Ferguson, the only one of the artists who while painting often kept spare tubes of paint in his pocket. Ferguson had absentmindedly pocketed a tube of white while creating the faked painting; it was the absence of that tube that Wimsey had noted at the start. The police are sceptical, but Wimsey offers a reconstruction, and over the course of twenty-four hours demonstrates how the killer established a false alibi: he ensured that he was seen boarding a train to
Glasgow, disembarked before the train left the station, staged the scene above the stream and faked Campbell's painting, bicycled to another train station, and took a quicker train to Glasgow, ensuring that he would arrive in Glasgow as expected and be presumed to have been on the first train when the painting was staged. Ferguson confesses, but states that Campbell's death happened accidentally during a fight, and was not murder. When the case is tried, the jury brings in a verdict of
manslaughter, with a strong recommendation to mercy on the ground that "Campbell was undoubtedly looking for trouble". ==Principal characters==