Witherton puts a request in for compassionate leave, a paperwork mix-up sees an unlikely candidate volunteer for a dangerous mission, and Potts causes mayhem in the map room.
German voices are heard in the corridors, Witherton dyes secret papers in an effort to find a leak, and the Ministry of Information bribe Potts to distribute leaflets about careless talk.
Potts is told to collect the regimental mascot, a problem with letters means a Nazi is sent to a swanky hotel, and General de Gaulle's aide insists on defending French honour.
There's a problem with the books in the library, Potts is arrested while collecting items from Witherton's house, and an idea comes from a note on the cell wall.
Petrol coupons are going missing, Potts is given the job of wheeling around a dummy of Churchill, and a French Resistance agent is en route to identify an assassin.
McRuckus is on the lookout for black marketeers, Witherton receives information about a jamming device above the map room, and a bomb lands in the bunker.