Frances brought everything together in a novel the result was hugely satisfying. It should however by this stage be apparent that this aim was not routinely achieved, and it is perhaps therefore fitting that Corruption should end the Fourth Series by illustrating both characteristic strengths and weaknesses that often surfaced in the later Janson books. The central theme, comprising a high-class call-girl racket used to obtain tendered contracts, is generally handled in an engaging manner, avoiding a neat imaginary resolution in favour of a far more convincing "public interest"-driven moratorium on news coverage. Moreover, Frances's writing had by this time achieved a level of competence whereby pace could be maintained without recourse to the graphic levels of violence used to bolster the narrative of earlier books. All told, the tale of Corruption contains enough twists, turns and engaging digressions to provide an entertaining read. The problem is, just as with the sexual-enslavement episode in Amok, that Frances seems compelled at times to introduce sub-plots that are not only unnecessary but also inexplicable. While Janson had a history of engaging with women who cried foul at the very moment passions ran highest there was always a rational ulterior motive for their behaviour. Yet no such motive emerges in the case of Janson's relationship with Mrs. Ralph, who appears possessed of insatiable desire only just as suddenly and fiercely to reject his advances (before or after intercourse is never made clear). This bizarre mode of behaviour leaves Frances once more struggling to construct around it a plausible dialogue.
The opening scene finds Janson present at a corruption trial in which a City Administrator, Dugdale, surprisingly offers no defence against the charges laid before him. Dugdale's daughter (referred to throughout, rather primly, only as "Miss Dugdale") later tells Janson that her father was the victim of a call-girl racket that is systematically engaged in corrupting city officials. In an apparently unconnected event, he witnesses the death of a drugged man beneath the wheels of city traffic, retrieving a car key with telephone number that the victim dropped. Inspired by Dugdale's daughter's revelations about call-girls, Janson attempts to run a feature exposing vice, but has no success in infiltrating the high-class call-girl circuit. He does however meanwhile trace the dropped car key back to a Mrs. Ralph who, while claiming to know nothing of the dead man, encourages Janson's advances before offering a resounding rebuff. Janson leaves believing she knows more that she admits to. The vice articles prove to be taking effect when Janson is duped into calling in the police on what it transpires is a staged murder, the intention being to discredit him in the eyes of the police.
Still suspicious of Ralph, Janson follows her to a beauty parlour she owns, where he once more encounters Dugdale's daughter, this time claiming that the vice ring that snared her father is run from the beauty parlour. He meets Mrs. Ralph and (still under an assumed name) succeeds in getting an introduction to a call-girl. He also learns from the receptionist that Ralph had indeed met the traffic accident victim, while adding only that he came from Boston. On returning home he is once again tricked into calling out the police on a faked murder.
Janson meets and is charmed by his "escort", Laura, but is alerted by her disclosure that she is from Boston. Delving further, he confirms that she is the daughter of the dead man, Clements, who had traced her to Ralph's premises. Later, having identified her father at the mortuary, Laura agrees to help Janson expose the vice ring. He is then visited by a Mr. Jordan who offers evidence on Ralph, fearing that the vice-feature publicity will adversely affect his chain of brothels, but the pair are interrupted by one of the men who had previously faked the murders. This time the murder is real and Jordan is left dead with only Laura, lying in concealment, saving Janson from being implicated. The killer is traced back to Mrs. Ralph, who is arrested and charged with Clement's murder, while Janson's attempts to print the story are vetoed by the FBI on the grounds that their investigations are incomplete. The book ends with consolation being found in the arms of "Miss Dugdale".