Mr. Thirlwell uses them the same way for nearly as many interrupting and digressing pages of his own. As with his Shandean mentor, that is the point. “Sterne’s subject is digression,” he writes. “Therefore, in the end, no digression can digress from the subject: in Sterne’s novel, digression is impossible.”

True enough for “Tristram,” a masterpiece whose comic side trips, like Don Quixote’s, are both mockery and affirmation of a graver straight line running beneath. Mr. Thirlwell, whose impossibly young face beams from the book jacket with an air of Little Jack Horner extracting plums, gets frequently lost on his side trips.

He is something of a prodigy and, as such, unstoppable. In his torrent of digressive connections  he joins together Chekhov, Samuel Johnson, Samuel Richardson’s “Pamela” and Hemingway in the space of three dozen lines  there are times we feel we are losing headway and the page numbers are actually running backward.

But the plums are real, even if squashed by too much else. Mr. Thirlwell has several large themes that make their way insistently through his shoves and hops. One is an impassioned belief in the novel. “Although this is a history of ephemeral inventions,” he writes, “the novel’s history is also a history of objects whose value is durable and timeless.” Then he adds, “Sometimes I believe this.”

Image Credit... Alina Simonen

So there he is: impassioned, yes, and skeptical of the passion, as if skepticism were the contemporary version of a Victorian chaperon keeping an eye on a susceptible and hot-blooded charge. The charge keeps getting away, though, and Mr. Thirlwell’s digressions purposely allow it to. “That is my personal form of romanticism. That is the romance of this book,” he writes.