Jonathan Lee’s new novel, “High Dive,” dramatizes and reimagines the Irish Republican Army’s 1984 attempt to blow up Prime Minister Margaret Thatcher and her cabinet during the annual Conservative Party conference in Brighton. Given its premise, readers might be forgiven for thinking that the book is a political thriller, but anyone coming to “High Dive” expecting a cliffhanger in the tradition of Frederick Forsyth or Robert Harris will be disappointed. Lee is far more interested in character than plot. Instead of white-knuckle action, we get a sequence of exquisitely rendered set pieces. The result is a beautifully realized novel about the intertwining of loyalty, family, ambition and politics. Lee’s truest antecedent is not “The Day of the Jackal,” but Joseph Conrad’s “The Secret Agent.”

All of which isn’t to say that “High Dive” lacks tension or surprise. Its narrative works like the time-delay bomb that is placed fairly early on in the proceedings, slowly ticking away under the floorboards of the reader’s mind, getting louder and more fraught as the detonation approaches. The human and political casualties of the explosion are part of the historical record, but the consequences of the blast for Lee’s three central fictional characters are what draw us in.

One of that trio is the bomber himself, a young IRA munitions expert named Dan who joins the Provos in part to avenge his father, who was killed during a protest march. (In an author’s note, Lee explains that this imagined character emerged from speculation that the convicted Brighton bomber , Patrick Magee, may have had an accomplice.) Dan is analytical and unsentimental, “a distance man,” as his clandestine supervisor calls him, but also prone to loneliness and, on occasion, to self-destructive acts. There is something stunted about him, an impairment stemming from his murderous craft. He still lives with his mother, his siblings having all fled Northern Ireland. They are the lone Catholic family on a Protestant street where they are being steadily harassed from their home. Lee makes Dan both a chillingly credible assassin and a sympathetically dutiful son who attends to his aging mother.

Author Jonathan Lee (Tanja Kernweiss)

The two remaining members of Lee’s triad of protagonists are Philip Finch, better known as Moose, the deputy manager of the Grand Hotel, and his 19-year-old daughter, Freya, who is “relaxing back into the comfy disappointment of her life since leaving school.” She works part time on the hotel’s reception desk while yearning for more exotic locales. Her father, a former champion diver, with a failed marriage and abandoned careers in teaching and coaching behind him, is a lovable sad sack who works 70 hours a week and suffers from “the ifs of introspection.” He clings to his daughter even as he wants to help her leave home and redeem his own shortcomings. From experience, he knows that “unfulfilled ambitions pile up like the unopened post and can clutter a person’s life.”

The arrival of the prime minister offers Moose a chance for a promotion and Freya an opportunity to engage with the wider world. Only one of them gets the push they need.

Although the matters at hand — terrorism, mortality, failure — are weighty, “High Dive” carries itself with an admirable lightness. Lee is fond of puns, innuendo and double-entendre. The novel never becomes bogged down in the intransigent politics of the Thatcher era. Indeed, there are passages here that owe as much to “Fawlty Towers” as they do to Graham Greene. The humor is rarely at the expense of Lee’s characters, but rather serves to make them fully human and believable. Some of the author’s best lines are throwaways about secondary figures. The Grand Hotel’s bellman is rumored to have a picture of Bernard Sadow, the inventor of the wheeled suitcase, on his dart board at home. The hotel’s older patrons are memorably described as coming “from a world of corduroy and borrowed novels.” Freya, thinking of her absent parent, observes, “Some mothers threw parties. Mine threw crises.”

Now and then, Lee’s sure hand slips. Disappointingly, Dan’s boss, the IRA mastermind, quotes Shakespeare and Leonardo da Vinci like a standard movie villain. An eccentric character named the Captain, who curates a collection of objects dubbed “the Museum of Lost Content,” seems to have wandered into the novel from a Joseph Mitchell New Yorker profile. An apparently shallow surfer who courts Freya turns out, unsurprisingly, to have more depth than she initially thought.

But these lapses are rare, and their scarcity points up the extremely high quality of everything else in the book, including the satisfying way that the disparate stories of these three protagonists dovetail at the end. Long after the bomb goes off, long after I closed the book, I found myself wondering about Moose and Freya and Dan. That persistence of interest is a testament to how fully realized those characters are, and how astonishingly well executed this novel is.

Jon Michaud is a novelist and the head librarian at the Center for Fiction.

High Dive

By Jonathan Lee

Knopf. 336 pp. $26.95