Justin Cartwright is the author of more than a dozen novels, a sundry collection whose settings include the writer’s native South Africa, his adopted England, the Middle East, Hitler’s Germany, and Richard Nixon’s San Clemente. Now, here is “Lion Heart,” a novel that follows the fortunes of two more Richards: the present-day, 32-year-old Richard Cathar, whose friends call him Richie, and the 12th-century Richard I, whose admirers call him Lionheart. Richie’s late father, a druggie and a seeker, had been obsessed with Richard I, thus his son’s name. He had also written an (unfinished) biography of the king, showing that Richard and Robin Hood had become “bosom companions.”

For his part, Richie is unable to decide if the 12th-century Richard was “a giant red-haired mass-murderer, anti-Semite and sado-masochist or one of the greatest and most romantic kings of all time, a brave warrior and dab hand at the courtly songs of the langue d’oc.” His father based his findings on intuition. “People who take drugs often do,” Richard notes. “To them much is revealed through close, leisurely self-examination.” But Richie is a genuine scholar with a degree from Oxford. This suggests a rational mind, yet he comes to believe that Richard I had acquired a portion of the True Cross in a deal with Saladin and, further, that this sacred chunk of wood is still hidden away somewhere. Richie makes it his business to find it.

To this end, the book clops along on two time tracks, one following Richard I, the other following our narrator, Richie. When we first meet the latter, his girlfriend, Emily, an aspiring writer, has left him for a married, “beardy literary man.” Emily’s occasional appearances are excellently entertaining, giving rise to acerbic observations about the human fauna of 21st-century England, everything, in other words, that Cartwright finds fatuous. This includes writers, and Emily, though unpublished, has acquired “the aspect of a writer — serious, a little worried about where it’s going,” but conveying also “the comfort of belonging to a superior caste, the writing caste.” After all, “writing is still highly esteemed, even more so than reading.”

Richie travels to Jerusalem on a research grant, ostensibly to study Crusader art, but really to find the True Cross. He falls in love with a beautiful Canadian reporter of Palestinian extraction. It is a romance eventually blighted by her kidnapping and the revelation of an unrelated, but highly problematic secret. It’s a shocker, the sort of unpleasantness that novels of yore resolved in the same way they did rape: by delivering the comfort of death or life in a nunnery to the lady involved. In this way, at least, “Lion Heart” finds common cause with the past.

’Lion Heart’ by Justin Cartwright (Bloomsbury. 330 pp. $27) (Bloomsbury/Bloomsbury)

But that is to leap ahead. Richie, hot on the trail of the True Cross, comes across an ancient document that — as is increasingly the case in novels today — has been overlooked for centuries. Squirreled away in the Bodleian Library, it is a letter from Richard to Saladin, written on vellum in ye olde French, and key to the whereabouts of the True Cross. This lucky break makes up for a lot in Richie’s life and, though he has a nervous breakdown thanks to developments involving his girlfriend, he pulls himself together, has a sexual interlude with a psychiatric doctor, and goes to see his old Oxford tutor, who tells him to write about his quest for the True Cross.

The fact is, this novel doesn’t seem to know what it’s doing. Richard I and his posse of noblemen, among them some wily Knights Templar, show up in passages of italics every now and again. But their carryings on — fighting the Saracen, quarreling with each other, getting shipwrecked, being held hostage, writing troubadour verse — never resonate with the present-day doings. For all the meaning it confers, Richie’s quest for the True Cross might as well have been for Archimedes’s bathtub.

One of Cartwright’s best novels, “The Song Before It Is Sung” (2007), also passes back and forth between the present and past. In that extraordinarily fine and complex work, however, the historical passages concern the life and beliefs of one of the German officers involved in the attempted assassination of Hitler in 1944. This part of the story is subtly refracted through the eyes of a present-day character, and the entire work is deepened by an unobtrusive current of philosophical tension between idealism and empiricism. “Lion Heart,” on the other hand, is not fully constructed. Disappointingly and surprisingly given this author’s accomplishments, the novel’s two elements are held together by little more than the glue of the spine.

Powers received the 2013 Nona Balakian Citation for Excellence in Reviewing from the National Book Critics Circle and is the editor of “Suitable Accommodations: An Autobiographical Story of Family Life: The Letters of J. F. Powers, 1942–1963.”