He sees the American A380, with its hundreds of passengers, on its south east-diagonal, about to make the ninety-degree turn for the north-eastern approach to Heathrow, leading it to the Thames. He takes a few strides to the right and scans the south-eastern path, the Middle East and the Indian subcontinent thousands of miles beyond. There, unmistakably, a second, equally packed A380 is heading towards him. He shuffles to and fro to compare the increasing sizes of these two enormous steel birds soaring ever nearer. Their progress is remarkably uniform. He wonders if any pair of eyes, apart from the woman at Drayton, is seeing anything unusual. He imagines being in the cockpit seat of the co-pilot in the second plane – the one who knows; the one in whose seat he himself craves to be; the one who, a few minutes before, will have secured the double-locked cockpit door, raised himself from his seat to walk behind the senior pilot beside him; the one who, stealthily, speedily, will then have placed an electric flex around the neck in front and pulled it hard and silently tight.

He imagines sitting in the other cockpit of the first A380 where the two American pilots will be admiring the approaching river and the Shard itself as their auto-pilot flies them over London’s law courts towards Big Ben and the Houses of Parliament. Perhaps they are joking, making plans for the evening, preparing to put their hands up a hostess’s skirt. The plane flies itself, as it has done thousands of times before, with an inhuman precision and flawless functionality – seven or so minutes to landing and an afternoon and evening of opportunity lie ahead.

In the second plane, the co-pilot may take a glance at the lolling head and lifeless eyes beside him. Theirs was only a professional relationship after all and the concentration with which he must now apply himself allows no time for pleasure or regrets. He has practised the manoeuvre over and over again on the computer program they built for him. He is one line of the equilateral triangle heading towards its intersection; the second plane is the other. But he is operating in the four dimensions of space and time; because in the final stages he will be pulling up sharply from a thousand feet below, he must be that edge in front to compensate for the extra distance created by the elevation. It is simply a matter of mathematics, a subject at which he always excelled and contributed to his double first from Queen Vic’s. Curiously – he had not factored this in – at this very moment he can see its Gothic pinnacles down to the right. He takes the aircraft out of autopilot and assumes control. He sees the other plane across the river and above him. He eases right, off his correct Heathrow runway two path, to increase the angle of difference between them.