Dublin Zoo is a three-part thriller comprising three distinct stories seamlessly weaved into one compelling narrative: firstly the story of the parents of Harold Bradshaw, the book's main character; then the account of Harold's time in London as a young adult in the aftermath of his parents' death; and finally the story of Harold's insertion into France as a British agent during World War Two. The book employs a notable "teaser text" technique, whereby the narrative's first and second stories are dotted with Harold's reflections from the book's third story, ahead of this third limb taking 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 One soldier, Albert meets and marries Rita while in France. The family - Albert, Rita and baby Harold - returns to England after the war where Albert embarks on building a business empire. This part features Harold's growth into adulthood in Scunthorpe in England's northeast midlands during the inter-war years (and also explains the Dublin Zoo title). 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 at a court martial hearing 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 World War, the period of prosperity following, and the world's subsequent decline into economic catastrophe, capturing the latter event by reference to Britain's return to the Gold Standard in 1925 and four years later in 1929 the advent of the so-called Great Depression. The first part concludes with the death of Harold's parents, murder in his mother's case and his father's related suicide, and Harold as a young adult taking revenge for their deaths. With that, Harold is forced to flee from Scunthorpe to London, beginning the novel's second story. Once there, 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 his parents. Shortly after arriving in London, Harold encounters 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 Harold kills two mafia hoodlums in self-defence, only for British justice to miscarry and convict him of dual murders.

In an ironic twist, the judge who hands down his lengthy prison sentence (in fact in the book's opening scene) is the very same young lawyer who years earlier saved Albert's life at the court martial 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 at the same time war clouds begin to build over Europe. The final stanza opens with the advent of World War Two. Harold is released from prison when he is recruited by the British Special Operations Executive to undertake a mission in France, in Marseille his mother's birthplace, in part because of his flawless French language skills learnt at his mother's knee as a child in Scunthorpe. But Harold is in fact an unwitting pawn in a higher stakes game. Thus ensues a gripping story of intrigue, double cross, Harold's involvement in another brief love affair with an older woman, one who reminds him of Katrina, and the development of an unshakable male friendship. Events come to a head in a tense, powerful, edge of your seat climax in Marseille when among other things Harold is reacquainted with a hostile member of his mother's family.