Natalie’s new boyfriend, Francois, is keen to become involved in Lifeline, but Albert has doubts. Paul Vercors, the fanatical leader of a Communist cell in Brussels, wants to take over Lifeline, and tries to enlist the assistance of a colleague – Max. Meanwhile, the Communists continue their resistance activities and plant explosives on a railway line to derail a train. Unfortunately, the train’s passengers include Natalie and Francois, escorting evaders down the line.

Brandt receives a visit from his wife Erika, who asks him to let her and their children come to live with him in Brussels as it is becoming too dangerous to carry on living in Berlin with the increasing British air raids. Brandt tells Erika that his work in Brussels may soon be over, as he has successfully infiltrated Lifeline with an undercover agent. Word of this reaches the Candide, and Albert must face the grim possibility of killing all evaders currently in hiding to preserve the safety of the line. However, Max and Dr. Keldermans have an alternative plan to discover the identity of the infiltrator, but the scheme requires the assistance of Natalie’s uncle, Hans Van Broecken, who hates Albert and will not help Lifeline.

A British Wing Commander is badly burned after he has been shot down over Belgium. London wants him back urgently, but his facial injuries make it difficult for him to go down the line. He manages to get to Paris with Natalie as his guide, but Monique decides that if he is to avoid detection he must disguise himself as a woman for the rest of the journey. Meanwhile, Madeleine is ostracised for her relationship with Kessler, but finds a new friend in Monique. The Candide and its staff are targeted by terrorists for being collaborators, and Natalie and Max fear the worst when the Gestapo arrest Albert.

The Germans are out to capture a group of evaders, believing them to be responsible for the murder of an officer. One pair of evaders manages to contact Lifeline, while the other two throw their lot in with the Communists. Francois is determined to prove his worth as a Lifeline guide to Albert and Natalie, and decides to co-ordinate the journey down the line for all the evaders, approaching the Communists to take responsibility for the airmen against Albert’s advice. Whilst visiting the Communists’ hideout, Francois meets Max, whose true loyalties have begun to emerge in force.