When a young Royal Engineer Officer is killed trying to defuse a bomb, he is replaced by raw officer recruit Brian Ash. Ash is shocked to discover that his new unit, the 97th Tunnelling Company, is in fact a hastily formed bomb disposal squad. With the Blitz devastating London every night and making massive demands on Royal Engineers' manpower, he is to take command of 347 Section forthwith. It's not long before he's facing the real thing at close range, with his men looking on from a safe distance, making bets as to whether he'll go the same way as his predecessor.