Our book today is the unsinkable 1950 Patricia Highsmith masterpiece Strangers on A Train, which wastes no time in leaping straight to the area of crime-fiction that always fascinated her: motive. Mystery novels love to play with all three of the tenets of crime – motive, means, and opportunity – but every author finds his own fascination among the trio, and Highsmith, who seldom took responsibility for any of the horrible things she did in her life, was therefore naturally obsessed with why people do the things they do (one can only shudder at the mainstream novels she’d have written if the murder-genre paychecks hadn’t been so satisfying). Strangers on a Train is famously a book entirely about motive, and it’s premised on the uncanny ability of sociopaths to sniff out other sociopaths.

The marquee sociopath in the book is of course Charles Anthony Bruno, so immortalized by Robert Walker in the hit movie adaptation of the book. He encounters Guy Haines on a train, and the two of them get to talking – Bruno about his tyrannical father and Guy about his philandering wife. Both are young men, and Bruno – one of Highsmith’s most convincing characters, oddly enough – is extremely personable and outgoing; he quickly divines that both he and Guy have one central person in their lives who could do with a spot of killing.

And yet, what sane person would risk it? Killers invariably get caught and electrocuted, and the main reason they get caught is because some dogged policeman pieces together the connections between the killer and the killed: who wanted the victim dead? Who might have benefitted from it? Draw up a list of those people and then sift the list according to who had the means to carry out the crime – who owned a gun? Who had the requisite garroting skills? And then once you’ve got that shorter list, you sift it again, this time for the people who had both the motive and the means and also the opportunity – not just the riflemen on the list but the riflemen who were anywhere near the victim at the time of the crime.

Highsmith gives Bruno a brainstorm: what if two random strangers who happened by pure chance to meet on a train were to swap murders? There’d be nothing – except the meeting itself – connecting the perpetrators with their victims, and hence no chance of a dogged policeman making any incriminating connections.

Guy laughs the whole suggestion off, but he accidentally leaves a book behind on the train, and Bruno takes that as the opportunity to write Guy a letter offering to return it  – and lightly alluding to his idea of swapping murders. The carefree tone of Bruno’s letter tugs at Guy, who’s feeling very hemmed in by his well-meaning family and his loutish wife. “It was pleasant to think of Bruno’s freedom,” we’re told, and he sits down to write a response:

A sudden impulse to write Bruno made him sit down at his work table, but, with his pen in his hand, he realized he had nothing to say. He could see Bruno in his rust-brown suit, camera strap over his shoulder, plodding up some dry hill in Santa Fe, grinning with his bad teeth at something, lifting his camera unsteadily and clicking. Bruno with a thousand easy dollars in his pocket, sitting in a bar, waiting for his mother. What did he have to say to Bruno? He recapped his fountain pen and tossed it back on the table.

As anybody who’s enjoyed the aforementioned movie will know, Bruno’s mad idea eventually does ensnare Guy, who soon enough finds himself in the nightmare moment of standing in the late-night bedroom of Bruno’s sleeping father:

The gun was in his hand already, aimed at the bed that looked empty however he peered at it.

He glanced at the window over his right shoulder. It was open only about a foot, and Bruno had said it would be open all the way. Because of the drizzle. He frowned at the bed, and then with a terrible thrill made out the form of a head lying rather near the wall side, tipped sideways as if it regarded him with a kind of gay disdain. The face was darker than the hair which blended with the pillow. The gun was looking straight at it as he was.

(Highsmith is a writer who’s been rather egregiously over-praised in the last twenty years, mostly by New Yorker-type deadline hacks who periodically try to liberate decent prose stylists from the shame of genre-writing, but even so, she’s very frequently capable of nifty details, and one of them happens in this scene, when the hovering, nervous Guy briefly hears a snatch of distant laughter away someplace in the nighttime neighborhood – it’s genuinely chilling)

And the neat rhetorical trick running through Strangers on a Train is the steady, systematic undermining of our confidence that we know who the crazies are – Highsmith subtly reminds us of the point we started with: that sociopaths have an uncanny ability to sniff out other sociopaths. As the book gathers momentum, passages like this one happen more and more often in Guy’s head:

But there were too many points at which the other self could invade the self he wanted to preserve, and there were too many forms of invasion: certain words, sounds, lights, actions his hands or feet performed, and if he did nothing at all, heard and saw nothing, the shouting of some triumphant inner voice that shocked him and cowed him.

This is one of the twists that still manages to animate this sturdy old book even after all this time, this and the fact that, swapped murders or not, there’s always the fascination of watching those dogged policemen at work. They can’t help it, and neither can we.