Spring, 1943. Sammy Rice is a bomb disposal expert with a tin foot and a grudge against the world because of it, and because he is in love with a girl, Sue, who he suspects loves him out of pity. To make things worse, Sammy is an alcoholic, with a taste for Highland Whisky. Sammy's conscience is also troubled by some of the bureaucratic intrigue that his employer, the Ministry of Defence, is trying to play down in an effort to win the support of the armed forces for the new Reeves Gun.

The Germans appear to have the advantage in the war, and are dropping a new anti-personnel bomb on innocent victims and unsuspecting children. Captain Stuart has been assigned to find out more about the mysterious bomb and its operation.

It is not long before he is introduced to Sammy at the Lord Nelson pub. Sammy is sympathetic to Stuart's difficult task, and the pair eventually head for North Wales where they attempt to learn more about the flask shaped anti-personnel bomb, which has just snagged its latest victim. Back in London, Sammy seeks the advice of the nervous but clever Corporal Taylor, who suspects the bombs may be detonated by a trembler device.

Preoccupied with this information, Sammy gets his nights mixed up and spends a lonely and agonising evening in his flat waiting for Sue to arrive home, while he goes mad with rage and is almost driven to drink. He discards his painkillers and crushes them on the floor with his tin foot.

Having confronted his alcohol craving, Sammy confronts an even greater challenge as Colonel Strang  briefs him on two further bombs that have landed on the shingle beach at Chesil Bank, Weymouth in Dorset. One of the bombs has already gone off, killing Captain Stuart while he was trying to defuse it. The second bomb waits nearby for its next victim.

Sammy proceeds cautiously, listening to Stuart's notes, as dictated by the ATS Corporal. Unknown to Stuart, Rice discovers a second trembler fuse as he lies next to the bomb on the beach. In a battle of nerves he eventually manages to defuse the bomb, to the relief of onlookers and Colonel Strang.

Having secured the confidence of Colonel Strang and the armed forces as a capable bomb disposal expert, Sammy is now in a better position to head the research unit. He tells Sue of his promotion and they embrace. She offers him a drink - something he can confidently resist now that he has finally made something of his life.