In the intricate weave of Spy Line, the tapestry is dominated by three compelling figures. Bernard Samson stands at the forefront—a taciturn, robust man nearing forty, sculpted by his middle-class roots. Born of a legacy of espionage—his father and Uncle Silas Gaunt both served the Secret Service—Samson grew up amidst the vibrant streets of Berlin. Fluent in German, English, and Russian, he embodies the quintessential English citizen, residing in a modest suburban London home. Formerly a field agent of unparalleled skill, Samson transitioned to a senior post at the German Station despite lacking formal university education, having instead cultivated a self-taught acumen.

His partner in life and intrigue is Fiona, daughter to a ruthless industrial magnate reminiscent of a modern-day Bounderby from Coketown. An Oxford alumna and fiercely autonomous, she too plies her trade in the shadows as a Secret Service operative. Together, they have two children. As the narrative of Spy Line unfolds, the echoes of Spy Hook (1988) linger, revealing Samson's mission to unmask a mole within SIS. This mission inadvertently exposes "Operation Hook," unveiling a shocking truth: Fiona, his own wife, is suspected of being a KGB double agent. Her defection to East Berlin plunges Samson into disgrace, his loyalty questioned by his superiors, leading to a warrant for his arrest. Thus, he finds himself a fugitive, seeking refuge in the shadowed quarters of Kreuzberg, near the formidable Berlin Wall.

With Fiona's departure from the heart of London Central, the children are left bereft of their mother. In this void, Samson enlists Gloria Kent, a London Central employee, to care for them. A Hungarian refugee and the daughter of a dentist, Gloria is a captivating blonde who seamlessly integrates into the Samson household. Despite the years that separate them, she and Samson form a connection, her affection for him growing profound. Samson, feeling the absence of Fiona's presence, reciprocates these feelings, though society casts a skeptical eye on their age disparity, questioning his aptitude as both husband and father. Yet, gossipers will always abound.

Within the pages of Spy Line, the tangled fates of these characters are laid bare, each twist of destiny altering their lives with ruthless intensity. As the saga nears its climax, Samson finds himself entangled in a perilous firefight, orchestrating Fiona’s escape to the West—facilitated by a grim sacrifice: her sister Tess’s life. Tess's remains are manipulated to masquerade as Fiona’s, allowing the couple to be whisked away to southern California, where debriefing awaits. Here, the truth unfurls like a puppet master’s plan—Fiona’s defection was a meticulously crafted ruse by the Department, a covert operation tracing back to her days at Oxford. In this grand chess game, Samson was but a pawn, while Fiona reigned as the Queen. Though the Department may have achieved some hidden objective, the personal cost is devastating. Samson’s career lies in ruins, promotions denied, despite his integrity perhaps being restored. His marriage is fractured, Fiona’s psyche irrevocably scarred, and his bond with Gloria shattered, leaving the future of his children shrouded in uncertainty.

As the trilogy concludes in Spy Sinker (1990), the narrative lens shifts to Fiona's perspective. Here, Deighton attempts a narrative technique that falters, depicting her as a "surrogate male," yet simultaneously captured in bouts of tears and self-reproach, a portrayal that struggles to resonate.