Dublin Zoo is a dynamic thriller blurring fact with fiction as it seamlessly weaves its three distinct stories into one, yet also a novel that grounds the reader before beginning to stretch imagination. The book is further notable for its "teaser text" technique, whereby its first and second stories are dotted with the lead character Harold Bradshaw's reflections from its third part, ahead of this third limb taking over and steering the narrative through to its gripping conclusion.

Harold's parents, Albert and Rita Bradshaw, are an Englishman from Newcastle upon Tyne and a Frenchwoman from Marseille. As a World War I soldier, Albert meets and marries Rita while in France. Faced with Rita's hostile family, her brother Axel especially, Albert, Rita and baby Harold settle in England after the war where Albert embarks on building a business empire. This first part features Harold's growth into adulthood in Scunthorpe in England's northeast midlands during the inter-war years. It is a tale dominated by Albert's rise from rags to riches and back to rags again, and concurrently, Rita's slide into mental illness. It also introduces the young lawyer who represented Albert when he was court-martialled during the Great War, saving his life, and who later becomes the guiding hand behind the establishment of Albert's business empire. The segment graphically depicts the global recovery from the First War, the period of prosperity following, and key events preceding the world's slide into the Great Depression and economic catastrophe.

The first stage concludes with the death of Harold's parents - murder in his mother's case and his father's related demise - and Harold taking revenge for their deaths. With that, the young Harold is forced to flee to London, launching the novel's second act. Once in the capital, he embarks on a series of action-packed exploits as he seeks to find his place in the world. Harold's destiny is shaped by a unique ability to calmly and calculatedly inflict violence and his ever-present worry of being called to account for taking matters into his own hands when avenging the death of his parents. Shortly after arriving in London, Harold meets Katrina, an older woman with whom he falls in love. But his affair with Katrina is as brief as it is intense. It comes to an end in 1937 when British justice miscarries and Harold is convicted of two murders. In an ironic twist, the judge who hands down his lengthy prison sentence (in the book's opening scene, in fact) is the same man who, as a young lawyer, years earlier saved Albert's life in France and later guided the birth of his business empire. This second story concludes with Harold incarcerated and facing at least eighteen years in prison, while concurrently war clouds build over Europe.

The final stanza opens with the onset of World War II. Harold is released from prison when he is recruited by a secretive British unit ostensibly to undertake a mission in his mother's birthplace of Marseille, primarily because of his flawless French language skills learnt at her knee as a child in Scunthorpe. But Harold is in fact an unwitting pawn in a higher stakes game entailing a secret British plan to exploit a traitor within the French Resistance in pursuit of a critical strategic objective. Thus ensues a gripping story of intrigue, double cross, Harold's surprise romance with another older woman, and an unshakable male friendship. Events climax in Marseille in an engrossing, edge of your seat characterization of the book's Dublin Zoo title.