Tom Yately, Stanley Baker, has just returned from time abroad and is eager to land a job as a truck driver with Hawletts, a tough haulage company. Cartley, [William Hartnell], the depot manager, lays out the brutal rhythm: drivers haul ten-ton loads of gravel over bad roads, with a minimum of twelve loads a day and the threat of being fired if they fall behind. Each run is 20 miles round trip, and the top driver can log eighteen runs in a day.
Tom meets the other drivers, including Redman, [Patrick McGoohan], the foreman and head driver. Lodging at the same house as the other drivers, Tom is befriended by Gino, [Herbert Lom], an Italian driver who is in love with Lucy, [Peggy Cummins], Cartley’s secretary. Red offers a £250 gold cigarette case to anyone who can outdo him in the number of runs, and Tom is determined to try; however, he soon learns Red has kept his place at the top by taking a dangerous shortcut that no other driver is willing to risk.
One evening, the drivers go to a dance at a hall and start a fight. When the police are called, Tom flees the scene. Red calls him a coward and, from then on, the other drivers (except Gino) bully Tom, hindering his runs and calling him "yellow belly." Despite this, Tom does not retaliate.
Tom visits his brother Jimmy Yately, [David McCallum], and his mother, [Beatrice Varley], in their tobacconist's shop. His mother refuses to accept money from Tom, blaming him for Jimmy’s life-changing leg injury that requires him to use crutches.
When the drivers collect their pay packets, Tom realises he has been underpaid. Red informs Tom his wages were docked to replace equipment damaged as a result of the drivers' bullying. A fistfight ensues, in which Tom beats Red. Gino offers to switch truck numbers with Tom the next day, so that the others can unwittingly harass Gino and therefore help Tom win the cigarette case.
That night, Lucy breaks up with Gino. Expressing her feelings for Tom while he performs a vehicle check, Tom confesses that he had not actually been abroad but was instead serving a year-long prison sentence. Lucy drops off Tom at the drivers' digs, both unaware that Gino has seen them from a window.
The next day, Tom purchases a one-way train ticket to London. Lucy rushes into the waiting room and reveals that Gino has been injured in a crash. Distraught, they rush to the hospital. While they wait outside Gino's room, Lucy says that Cartley and Red have been scamming money by hiring five fewer drivers than the company pays for and pocketing the difference. A doctor later reveals that Gino is dying. Gino switched the truck numbers as arranged, and tells Tom "I threw them off like we planned, for you to win. Crazy. You don't even come." Tom asks if it was Red who caused his crash, but Gino dies without answering.
Tom returns to the depot and confronts Cartley. He says that Gino died and that the scam had been the reason. Cartley offers him a share of the stolen money and Red's place in truck 1. Tom reluctantly takes truck 1 to pick up a load. When Red turns up, he forces Cartley to join him in what they think is truck 3 and sets out to silence Tom. Red guesses that Tom will take the shortcut, and they lie in wait there. When Tom appears with his truck full of ballast, Red starts sideswiping him, forcing him off the road and onto the edge of a quarry, where the truck dangles, with Tom knocked unconscious. But the brakes on Red's truck, which Red realises is Tom's truck 13, fail; he and Cartley drive off the edge and die. Tom wakes up and escapes before his own truck tumbles into the quarry. Lucy, who followed them in a jeep, runs to him.
