Excerpt from Timekeepers by Simon Garfield, plus links to reviews, author biography & more

Perhaps you can imagine the train coming down the track on Sunday 3 July 1938. The engine, tender and cars are blue, although whether you'll be able to see this as it speeds past you is questionable. There is also a rickety brown carriage early in the chain, known as a dynamometer car, and within this are men with stopwatches and machines that resemble primitive lie detectors and heart monitors. The train is travelling so fast that it appears to be 'hunting', the phrase engineers use to describe a locomotive hurtling at such a velocity that it is swaying from side to side, as if it was searching for the fastest route to its destination, happy to jump to another track if need be. Its destination is London, but it will overheat long before then.

You are watching the train from Stoke Bank, not far from Grantham. The threat of war hovers. Twelve-year-old Margaret Roberts is at school up the road. The hurtling train, and its memory, will swiftly become one of those iconic prewar images, like the last of the country house shooting parties before Britain went dark. What it is about to do will never be bettered, and the anniversaries – 25th, 50th, 60th and so on – just can't come soon enough. People who love trains love this train as much as they love anything.

Similar locomotives in this group, known as A4 Pacifics, were designed to look and perform like Mallard, and their engineer Nigel Gresley gave them all similar names: Wild Swan, Herring Gull, Guillemot, Bittern and Seagull. But to Gresley – 62, failing health, his designs internationally recognised and copied, his trains, including the Flying Scotsman, lauded for both safety and comfort, an engineer comparable in achievement to the Stephensons and Brunel - none of them appeared to be chosen like Mallard, with her dynamic lines and increased cylinder pressure, and her new brake valves, double chimney and blast-pipe maximizing steam production.

At Stoke Bank it has its chance. The ride through Grantham has been slow due to track maintenance, but it has reached Stoke Summit at 75 mph and accelerates now over a long downhill stretch. The speeds at the end of each mile from the summit were recorded as: 87½, 96½, 104, 107, 111½, 116 and 119 mph the subsequent half-mile readings then gave 120¾, 122½, 123, 124¼. And so Joe Duddington, aged 61, an Englishman based in Doncaster, employed by the London and North Eastern Railway since its formation in 1921, and Mallard's driver that day, pushed her on a little as she thundered past the Lincolnshire village of Little Bytham. 'She just jumped to life like a live thing!' he would recall a few years later. 'Folks in the [dynamometer] car held their breath.'  The train achieved a top speed of 125.88 miles per hour, a steam record that stands to this day.

Time passed. Seventy five years later, a great gathering of 90 old-timers gathered at the National Railway Museum in York to talk of crewing the Mallard and manning the sheds, and to tour another great gathering in the main hall, all six of the surviving A4 streamliners (of 35 built), huge and gleaming, a product of England: Mallard, Dominion of Canada, Bittern, Union of South Africa, Sir Nigel Gresley and Dwight D Eisenhower.  They were all wonderful engines, but the Mallard had the celebrity status – the fastest, the only one purchasable in 130 parts, its creator's favourite - and it did seem to glow more than others, the way Marilyn Monroe or Cary Grant used to. And like movie stars, adults who should know better sighed in the train's presence, as if they weren't worthy, as if the train was of a different and higher species. Iron and man-made as it was, it was also a deity, shining huge above us. I queued up to step on its boiler plate, and I would have put on overalls and cap and begun shoveling coal if they'd have let me.

Excerpted from Timekeepers by Simon Garfield. Copyright © 2017 by Simon Garfield. Excerpted by permission of Canongate Books. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.