Whilst dining at the Candide, Kessler becomes intrigued by Madeleine Duclos, an elegant but remote socialite. Meanwhile, Monique takes some airmen down the line and is shot and wounded when she becomes unintentionally involved in a smuggler’s attempt to evade a railway checkpoint. Recovering in a convent hospital, she is cleared of smuggling, but finds herself in more danger when the French police discover the train tickets she was carrying for the airmen and that her papers are false. Kessler sets out from Brussels to interrogate her, prompting Natalie, Alain and Max to stage a daring rescue mission.

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.

Kessler is enjoying his developing relationship with Madeleine, but begins to feel that his feelings for her may cloud his judgement while Brandt is once more approached about joining the military plot to assassinate Hitler. The British co-ordinate a massive air raid attack on Berlin, but bombs are dropped on civilian targets in error – with tragic repercussions for Brandt. Monique and Alain try but fail to help a bomb aimer shot down on his way back to England. Having captured the man, Brandt finds himself face to face with the enemy and this time, it’s personal.

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.

At Gestapo headquarters, Kessler takes an instant dislike to the newly arrived Luftwaffe Major Hans Dietrich Reinhardt, who has joined him in a final concerted attempt to crush the evasion lines. As the Allies continue to advance from the invasion beaches, Lifeline must continue their efforts in getting airmen back to Britain, but when Natalie attempts to guide two evaders down to Spain, it becomes clear that their work may at last be over.

Lifeline’s original function is now over – the Allied advance has severed the evasion lines and it is now a matter of keeping evaders safely hidden until the war is over. Despite Kessler’s irritation at Reinhardt’s manner and methods, his efforts pay dividends when he discovers a Lifeline safehouse. Two of his new prisoners commit suicide rather than talk, but Reinhardt is determined that the third prisoner will give information under torture. Albert and Monique receive a tip-off that the middle-aged Chantal sisters, who are based in Senlis and often shelter airmen for Lifeline, are in imminent danger.

An assassination attempt has been made on Hitler, and Kessler believes that Reinhardt is involved in the conspiracy. He begins to gather information that he hopes will provide his colleague’s guilt. Meanwhile, Albert becomes aware that the Communists are once more out to get Lifeline, and that he is their target.

Bradley travels to the Ardennes to continue recruiting his own private army of former airmen to engage in sabotage activities – the target is V2 testing sites. Bradley’s first objective, however, is to hijack a convoy of weapons and he asks Monique for assistance in recruiting men and resources. Lifeline, previously an evasion network, is now a fully-fledged guerrilla operation

As Bradley’s army remains in hiding along the Dutch border, he and Natalie become closer as they work together planning the raid on the V2 site. To increase his chances of success, Bradley must try to obtain the rocket delivery schedule and plans to get the information by dining with Kessler at the Candide…. Meanwhile, Reinhardt is rapidly closing in on Lifeline, with Natalie as his chief suspect.

The Allied advance continues as they at last enter Belgium, and the Germans begin to plan a strategic withdrawal from Brussels. Albert is petitioning for his release from prison, while Bradley endeavours to forge links with other resistance groups. The people of Brussels are now left to their own devices, and recriminations are brewing for collaborators and black marketeers. Kessler comes to help Madeleine, while Alain offers Monique and Natalie a place to hide. Meanwhile, Reinhardt at last obtains proof that the Candide is Lifeline’s base of operations, and prepares to strike.

Albert is finally released from prison and reunited with Monique. The Lifeline personnel continue to be in danger of reprisals from their own people and the Communists for alleged collaboration with the Germans, but Albert refuses to leave the Candide. The Allies are still making their way towards Brussels, and Natalie and Alain join the offensive. As Kessler and his men leave the city, Reinhardt stays behind to complete his investigation into Lifeline and pays one last visit to the Candide, just as Paul Vercors emerges to take ultimate revenge on Albert.

Vercors has taken Albert, Monique and Reinhardt prisoner, and plans to hang Albert as a collaborator and a murderer. Only the Allies, helped by Natalie, can save him but they have only just entered Brussels. Meanwhile, Kessler and Madeleine are trekking on foot towards Germany through the Belgian countryside. To evade capture by the Allies, Kessler decides to take on a new identity.

Kessler, still posing under an alias, and Reinhardt find themselves interned in the same prison camp for German officers. Kessler learns that Reinhardt surrendered himself to Albert at the Candide and is determined to dispose of him with a trumped-up court martial. Madeleine is forced to make a decision that will change her life forever. In Brussels, Albert and the others learn they are to be decorated for their selfless contribution to the war effort and Albert is given full ownership of the Candide as a reward for his bravery. However, it is a bittersweet victory for Albert as he has lost Monique, who is about to marry Captain Durnford and leave for a new life in England. The Second World War is over.