This has all the hallmarks of a good Rendell novel. We have a protagonist with a disturbed mind, approached in close third person, allowing us to get inside the wonky thoughts. Victor Jenner has just been released from prison after 10 years for attempted murder. He’s also, and more importantly, a serial stranger-rapist, though has never been tried for that. He is not right in the head; his sense of what the world owes him, and what he owes the world, is fatefully askew. We have the protagonist set in a situation from which no good will come. Victor strikes up an unlikely relationship with his victim, David Fleetwood, and his girlfriend, Claire Conway, and meanwhile exploits the carelessly attended cash lying around his aunt Muriel’s house, and meanwhile tries to resist raping anyone. And so we have the creeping sense of dread as we wait to see exactly how nothing good, and something terrible, will come of this situation.

And yet, somehow, this did not seem very good. It’s illustrative of the problems of writing about essentially mad characters in crime and thriller novels. One of the principal sources of interest in such novels is motive. Exploring why people do bad things allows the author to explore dark byways of human thought and behaviour. But that exploration depends on a sort of baseline assumption of rationality. If the reason your character does bad things is, basically, that they’re mad, the exploration has much less interest, and you seem to be left with two choices: either provide no explanation at all of their behaviour beyond madness, which is shallow and unsatisfying, or provide an explanation of their madness, which has risks I’ll mention shortly.

What Rendell often does well is occupying an uneasy middle ground between those two choices. She provides detailed and forensic descriptions of patterns of disturbed thought, while refraining from offering any explanation or judgement of the disturbance. The description provides enough explanation to satisfy, and also gives an opportunity to demonstrate an authorial gift for precise and believable descriptions of this kind, and also, because the thoughts are disturbed, gives the reader a sort of visceral sense of nastiness akin to the one you feel looking closely at a bad physical injury.

The thing with this novel is, Rendell doesn’t do this well. She strays too far in the direction of trying to provide something like an explanation of why Victor’s mind is disturbed in such a way as to make him a rapist (this, rather than the attempted murder, is his real crime and pathology). But she doesn’t go far. Instead she gives a whole load of hinted, teased, possible explanations, and then sort of shrugs and tells the reader to make of that what they will. There’s some stuff about the relationship between Victor’s parents, and the fact that he saw them shagging while still quite young. Was that it? Maybe. There’s a suggestion that 10 years in jail would send anyone mad. Perhaps? There are gestures towards awkward formative moments in relationships with women. There is, bizarrely, a phobia of tortoises. There are lots and lots of descriptions of dreams (always a bad sign) that are perhaps supposed to reveal something about his subconscious. And so on.

The central problem here is that none of this amounts to a serious attempt at explanation of disturbance. There’s no theoretical cogency, no consistent line, just a messy knot of things that might have the makings of an explanation. That’s far from ideal. But it’s one of the risks of starting down the path of providing explanation of your protagonist’s madness. Either you really go for it, in which case you have to essentially give the reader a psychology textbook, or you hint at explanation and hope it convinces. The former is likely to be dry, and beholden to some particular theory that the reader may dislike: the latter is likely to be unsatisfying in exactly the ways that this book is.