JONAS BONNER is a week or two into recovering from a suicide attempt. Diagnosed as clinically depressed, medicated, and in a psychiatrist's care, he is convalescing at his parents' suburban home when he is visited by his enigmatic uncle DAVID ROSS, long ostracized from the family for reasons which those of his generation will not explain. While David's initial attempts to empathize with his suffering nephew are rebuffed, Jonas does take come to take him up on an offer to reside with his uncle in London for a while. David is staying at the home of his deceased parents, preparing to lease the house to tenants in the coming summer, this effort no small cause of friction between him and his two older sisters, Jonas' mother Margot and Aunt Charlotte.

Uncle and nephew as virtual strangers to one another, David is reluctant to allow Jonas to stay long-term in the house, but relents at Jonas' half-hearted pledges to better his health. Previously Jonas had enjoyed a prodigious musical career as co-principal oboe with the London Symphony Orchestra. Mental and physical breakdowns brought about the loss of both his job and his romance with girlfriend EMILY. David sets the condition that Jonas must attempt to resurrect his musical career if he is to remain at the London house. After witnessing an inexplicably hostile confrontation between David and an enigmatic hairstylist, FABIAN JACHS, then an ugly argument between David and his mother, Jonas determines to learn the reasons behind David's estrangement from their family.

David begins to unfold piecemeal to Jonas the events of his teenage and early-twenties years in the late 1960s and early 1970s, a stormy tale centering around particular women employed at a Soho strip-club called the Andromeda Room, and David's own management of the BABYLON nightclub, a spectacular, ritzy hot-spot that featured a scale replica of the famous Ishtar Gate and a dance hall designed after the legendary Hanging Gardens. David is still troubled by the loss of his then-girlfriend JIA, a dancer at the Andromeda Room who was entrapped by heroin addiction and disappeared to her apparent death not six months after David rejected her for her total failure to shake her drug habit. These tales Jonas can hardly believe, for his straight-laced, prosperous businessman Uncle David seems nothing like the dazzling, flashy young David of Babylon, and the nightclub itself, while documented in photographs and news media, sounds to him nothing short of lavish fantasy.

From the very colorful and staunchly nocturnal Fabian, Jonas acquires different, darker perspectives on London by night, and David's past, discovering that as a teenager Fabian functioned as a prostitute called LOKI. From his sister SARAH's newspaper archive research, Jonas finds out that just months after his own birth, his uncle David was imprisoned for the manslaughter death of his business partner in the Babylon nightclub.

While struggling to get his musical career back on track and cope with lingering feelings for his ex-girlfriend Emily, Jonas is introduced to the mysterious painter LYDIA THORNE, a visiting acquaintance and houseguest of Fabian's. Jonas becomes preoccupied with the exotic and beguiling Lydia, but soon after meeting her, a terrible row takes place between David and Fabian. Fabian accuses David of being at fault in driving Jia, once a friend of his, to her death. Having had a bit to drink at the time, David becomes enraged; the ensuing brawl is ended when, to Jonas' horror, Fabian displays amazing physical strength and a terrible pair of vampiric teeth.

David refuses to believe what supernatural facts his nephew's eyes have seen and Jonas confronts Fabian about it. To his morbid fascination he learns that vampires are quite real and Fabian's friend Lydia is a vampire as well. His fixation on the beautiful Lydia and her mutual interest in him overcome his fear of the bizarre reality he has been introduced to. Jonas and Lydia commence a torrid, weekend affair, and he is thoroughly infatuated with her. Nonetheless Jonas mocks David when his uncle expresses wistful, idealized memories of the long-gone Jia. Jonas quickly becomes bothered by Lydia's selfish, domineering behavior and her emerging attitude of superiority, as well as frustrated by the lack of future for their budding romance. He witnesses Lydia's condoning of a violent death and is repelled by her inhumane behavior, seeking human warmth in a tryst with his ex-girlfriend Emily. Soon after, Jonas discovers that Lydia is one and the same with his uncle's lost love, Jia. Furious and feeling used, he confronts her with this knowledge and they part ways, she returning to her home in Paris. Jonas determines to keep Lydia's identity to himself, unwilling to wreck David's time-sweetened memories of Jia.

Finding some amicable resolution with Emily and succeeding in reestablishing himself as a professional musician, Jonas is offered the second bedroom at David's own flat, a temporary place to live while he restores his good financial standing and independent lifestyle. He accepts, and determines to engineer a reconciliation between his mother and David. Achieving some success with that, he also restores his friendship with his sister Sarah, and is enjoying a greatly more healthful existence as David's flatmate when Emily invites him to an exhibition at the art gallery she manages, a showing of Lydia Thorne's work. Aware that Lydia never attends her own exhibits, Jonas goes and is shaken to encounter her there, along with Fabian, neither of whom he has seen since the end of his affair with Lydia some months before.

David arrives at the gallery with news that Sarah has been hospitalized after a car accident. David and Lydia find themselves face-to-face; Lydia flees and a stunned David gives chase. Fabian drives Jonas to the hospital. When Sarah has stabilized, Jonas and Fabian embark on several hours' trip around the city, searching for David and Lydia. David is found, emotionally battered, on the curb outside the former location of Babylon, having learned the whole truth about Lydia's disappearance so many years before. David is distraught at the shattering of his idealization of the woman he once so loved, heartbroken that she kept herself unknown to him for twenty-five years and let him believe she'd been murdered. Jonas reaches out to David, actualizing the friendship that his uncle originally offered, cementing the change for the better that each has made in their lives, and together they leave Babylon behind, severing the threads of the past with a hope for the future.