Knots and Crosses, which was published in 1987.
Rebus is considerably older by now, but just as cantankerous and just as grimly determined to pursue his own path to justice irrespective of what his superiors might think. A few years ago, Rebus reached mandatory retirement age and had to leave the force, but he managed to return as the member of a cold case squad, which was open to retired detectives. Now that the law has been changed, he is able to return to the regular force, albeit at a lower rank. The latter matters little to Rebus who is simply grateful to be back in the game.
As the book opens, Rebus is charged with investigating an auto accident involving the daughter of a wealthy and powerful businessman. The daughter, who is dating the son of a prominent politician, was found in the driver's seat of the wrecked car and insists that she was driving, that she was alone, and that she simply lost control of the car. But the circumstances surrounding the accident raise Rebus's suspicions, and he's convinced that there's something more sinister going on.
At the same time, investigators have reopened a thirty-year-old case involving murder and possible police corruption that centers on a group of police detectives who were known as the Saints of the Shadow Bible back in their heyday in the 1980s. It was a different day and age, one in which detectives sometimes coerced confessions, planted evidence and administered their own brand of justice. As a young detective, Rebus was initiated into the Saints, although as the newbie in the group he was not told all of their secrets.
Rebus winds up being both a potential target of the investigation into the Saints as well as part of the team investigating their activities. In this, he's teamed with Malcolm Fox, a member of the Complaints--the Scottish equivalent of Internal Affairs--and the protagonist of another excellent Ian Rankin novel, The Complaints.
Needless to say, the relationship between Rebus and Fox is a complicated one. Rebus shares the distain that most regular police feel for cops like Fox, and Fox doesn't know how far he can trust Rebus or if he can trust him at all. Rebus doesn't know if he's been included in the investigation simply as a means of incriminating himself along with his old pals or if Fox genuinely expects him to help solve the case.
Rebus is naturally caught between the rock and the proverbial hard place. He's the only member of the Saints still on the force and his old comrades expect that he's going to be true to his oath and protect them from being exposed. Rebus, though, is his own man and will follow his own path in both of these cases, irrespective of what Fox, his other superiors or the aging Saints might want.
All in all, it's a great read and one of the best books in this series. The dynamic between Rebus and Fox is very complicated and interesting, as is the relationship between Rebus and Siobhan Clarke, the woman he mentored for so many years and who now outranks him. The investigations are complex and Rankin keeps the tension building at just the right pace. No fan of the series will want to miss this installment and readers who have somehow missed the series will enjoy the book as well, although naturally they will want to read the first eighteen Rebus novels along with The Complaints before tackling this one.