Newly-promoted Second Lieutentant Brian Ash joins his new regiment only to find that they are assigned to bomb disposal in London. Ash is thrown in at the deep end when he and his men are sent to a bomb site.
Ash tackles a bomb that is not considered vital with a new fuse extractor that doesn't work properly. New Lieutenant Machin is placed with Ash to get some on-the-job training. Major Francis criticises Ash after a patriotic magazine article profiles 347 Section.
Ash and Machin are recalled to London from a bomb disposal course and attend to a bomb in a school yard that is dangerously close to a telephone exchange. When another bomb is uncovered close by, Ash reluctantly allows Machin to defuse the second bomb.
The UXB in a Soho nightclub can't be defused - according to the Germans. While the men of 347 Section pit their skills against German ingenuity, Ash (Anthony Andrews) receives a letter from Susan (judy Geeson), the scientist's daughter..
A new commanding officer's methods of discipline border on the psychotic, and the overworked men of 347 Section consider mutiny. Meanwhile, Ash and Susan discuss their future.
Ash learns how to dispose the new German land mines, thanks to the help of naval experts. The bad news is that Susan has decided to return to her husband.
Ash and the men of 347 Section tackle Hitler's latest deadly invention, the butterfly bomb, designed to kill a man at 25 yards. Meanwhile, Salt breaks orders again, but for the last time.
Are Ash's injuries too much to overcome -- or is it depression over the many lives lost? After being talked out of the hospital to defuse an "antique" bomb, he discovers it was a ruse to restore his confidence.
