The Fourth Arm

The French Resistance spot a new German weapons base being developed near Calais. Their sabotage attempt goes badly wrong while a Bomber Command mission also proved unsuccessful. SOE decide this needs a trained unit.

Returning from France, Gallagher begins to compile a team of specialists to train for a one-off mission behind enemy lines. Not everybody is convinced that some can be trusted to follow orders.

Gallagher hands over his new unit to Lt. Col. Squires to begin their training. Scientist Stephen Lovell might be the most vital person on the mission but the army intend to play hardball with him.

Training intensifies with the unit put under extreme interrogation methods to see how they fare. Macaulay's attempted night out becomes a cropper.

The date of the mission is pushed forward when SOE receives new intelligence that the Germans could have up to 14,000 rockets. Final selection is held before paratroop training begins in earnest.

Macaulay's position is in doubt when he struggles to overcome his fear on his first parachute. Rohr is informed that she will go into France as reconnaissance before the main group.

Following a nighttime jump, the unit rendezvous at Pierre de Grouchy's farmhouse. Meanwhile, Gallagher discovers a traitor in the Resistance while former nightclub singer Simone could be recognised.

After a successful first mission, the unit get debriefed; McKenzie is carpeted for his actions while Gallagher has to inform Simone's mother of her tragic death. Tightrope walker Soltysyk 'Warsaw' is recruited.

Gallagher wants to be relieved of duty due to attrition rates among the recruits. Lovell starts playing up, causing friction within the group. Meanwhile, Merle and Ferdy start planning a future together if they survive.

The unit has now been reduced to six specialists who will participate in the raid. Lovell is determined to quit but no replacement can be found. His superior Professor Evans is brought in to help change his mind.

The unit enters France and discover, from Pierre, that the invasion is a mere two days away. The group head to the German rocket base in Deauville. An RAF bomber raid causes the power to go out, allowing the unit to get in.