At forty years of age, Daniel Winter has just begun his career as a private detective, having been pensioned off by the Metropolitan Police (where he rose to the rank of Detective-Inspector), ostensibly on mental-health grounds. During his period of enforced leisure, he wrote and published a novel, the proceeds of which had given him the wherewithal to chance his arm as a private detective. To his new line of work, he considers himself peculiarly ill-suited.
On the day that he is commissioned to search Oxford for Miranda Ward-Homer, daughter of a wealthy Hampstead lawyer, Daniel learns that his close friend since childhood, Philip Haygreen, was found dead, hanged, two days before, in his home in the Jericho district of Oxford, apparently in suspicious circumstances. The fact that he and Philip have been estranged for fifteen years, owing to their long-standing rivalry for the affections of Sylvia Blackman, compounds Daniel's grief at the demise of his friend.
As he searches for Miranda (who, he learns, is known professionally as Dana), Daniel becomes aware - and not a little disturbed - that Philip and the girl knew each other, and that the death of the former and the disappearance of the latter are connected. Thus is he drawn into the sordid world of Oxford nightclub-owner Dane Goldman (known to friends and enemies alike as the Great Dane).
Daniel's unlikely sidekick is Kendal Waterhouse, the sixteen-year-old daughter of his former girlfriend Rosie. Kendal, embroiled in a troubled relationship with her mother, is staying at Daniel's flat for the summer. Not unnaturally, Rosie disapproves of the arrangement and makes repeated insinuations as to Daniel's motives for letting Kendal stay with him. Daniel protests that he does not want Kendal staying at his flat, and that, in any case, she is doing so only because Rosie and Kendal have such a combustible relationship.
Kendal is a spirited and intuitive girl, attributes which she harnesses not only to provide invaluable assistance to Daniel during the course of his investigation - his twin investigations, as we have seen - but also to fathom the whereabouts of his mother, Roseanne, who left the family home one October evening, thirty-two years before, never to return.
Indeed, the missing Roseanne is the third case which Daniel finds himself investigating simultaneously. A series of signs of a supernatural kind puts him on the trail of Roseanne, whom he has long presumed to be dead, or, at least, irretrievably absent from his life. With Kendal's help, Daniel interprets the signs and finds himself grappling with a startling discovery. His discovery fulfils one part of the pact forged between Daniel and Kendal: that she will help him find his mother if he helps her track down the father that walked out on her when she was a month old.
Sailing By contains three love stories. In addition to describing the father-daughter-like love between Daniel and Kendal, the story recounts the love between Albert Winter and his wife Roseanne, together with the love between Philip and Sylvia. None of these loves is entirely wholesome and at least two of them are doomed.
Daniel is both inspired and haunted by the love that had bound his parents since they were children, a love that he idealises, almost deifies. What was it about their love, he wonders, that caused his father to take his own life and his mother to walk out on her children three months thereafter?
About the love between Philip and Sylvia, Daniel has greater understanding, though he still has trouble working out how and why the virtue of his erstwhile friend was so corrupted by the dissolute Sylvia that he ended his life having inverted his personality and become a disfigured shadow of the man and the boy once he had been.