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 his first bomb.

Ash and Susan go off for a quiet weekend away but Ash is recalled to deal with an unexploded bomb and Susan returns home to find her husband waiting for her.

347 Section cooperates with the Royal Navy to deal with a bomb that has a 17-second fuse. Ash decides to ask Susan to marry him.

Ash is assigned to Cambridge to help Dr. Gillespie with the new Y fuse, and meets Susan again.

The Company packs up and moves to the coast where they are to clear the beaches of dozens of British mines laid in preparation for a German invasion.