Newly-promoted Major Francis takes command of the unit and proceeds to enforce new disciplines, but his chief target seems to be Ash and his men.

The Germans have been dropping a new butterfly bomb that are proving difficult to defuse. 347 Section is one of a number of units called to a small English village to deal with them.

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.

Ash convalesces after a near-fatal accident while defusing a mine. With his mobility severely impaired, he is to be reassigned to light duties away from the bomb disposal unit.