I believe that Florence: Or, the Aspirant (1829) may well qualify as the worst Victorian novel I have ever read. Yes, worse than Hawkstone, the previous winner. Or loser. (I should name that award. We need the Razzies for Victorian fiction, no?) Now, granted, nobody in Florence gets eaten by rats--not every novel can dispatch its villain with such efficiency, after all--but it boasts quite possibly the most inept plotting I have ever had the (mis)fortune to encounter. Volume I holds out the barest promise of a plot: there's poor, wrongly defamed Mrs. Stanhope on one side, the rabidly anti-Protestant Dr. Edmund Campian (good heavens!) on the other, and, in the middle, Florence, a possible love interest for Dr. Campian's son (also Edmund). Also, there's a 5'9'' sister who cross-dresses. Surely, there must be potential here somewhere. This being a Catholic novel, the innocent reader assumes that the elder Dr. Campian will learn the error of his ways and that the Stanhopes will convert. (The innocent reader experienced with Catholic fiction will know better than to expect a conventional romantic ending, however.) But, soldiering womanfully onward to volume II, the reader finds...a priest, carrying on a monologue about the essentials of the Catholic faith. Really. It's a monologue. For nearly the entire volume. (The women occasionally get a word in edgewise.) "Alas!" wails the innocent reader. "Where's the plot?"
Trudging onward into volume III, the aforementioned innocent (albeit somewhat disillusioned) reader makes an astonishing discovery: the elder Dr. Campian, he is kaput, thanks to a nasty letter that someone sent him about his son's probable interest in Florence. Yes, it's death by non-existent filial love interest. The priest (still carrying on) announces the death like so:
"...In the mean time a person gave a letter to the servant-maid for old Dr Campian, which she delivered immediately; and when Thomas returned, he found his master in a state of utter insensibility, or, to speak more truly, dead, and the letter lying before him on the table." 
To which the reader, stripped of all hopes whatsoever, can only say: "'Or, to speak more truly, dead'‽" (Prose this bathetic positively demands an interrobang.)
Bear in mind that it's been a few hundred pages since we've seen either Dr. Campian; in fact, we'll see neither hide nor hair of the younger one, ever again. Instead, we have yet more monologues from the priest, another monologue from a Catholic pit-man, and an inset narrative about a Catholic youngster who converts a sort-of ex-Calvinist and prepares to settle down and live happily ever after with her. "But who are these people?" wonders the reader, entirely demoralized. Matters come to a head with the appearance of Henry Howard's Remarks on the Erroneous Opinions Entertained Respecting the Catholic Religion. Not, it isn't a character; it's the entire pamphlet (as far as I can tell), reproduced in the novel's penultimate chapter. (Mrs. Robertson also does a liberal cut-and-paste number on Demetrius A. Gallitzin.) This novel does no wonders for copyright laws, let me tell you. At this point, the reader's gast is so flabbered that she can only gape in amazement when the novelist finally remembers...the plot! In the last chapter! ("I forgot the plot," says the reader, mournfully.) Mrs. Stanhope's persecutor appears, says nasty things about Catholics, and torches some books. Florence, however, holds firm. And...the end.
(That all being said, the novel does do some unusual things; in particular, there are lengthy discussions from a Catholic POV of eighteenth-century and contemporary fiction, including several paragraphs on Maria Edgeworth, Sir Walter Scott's The Monastery, and Grace Kennedy's Father Clement. Florence is a response to the last--which, for those of you wondering why on earth I would subject myself to such pain and suffering, is why I was reading it.)
 [Mrs. Robertson], Florence; Or, the Aspirant. A Novel (London: Whittaker, Treacher, & Co., 1829), III.2.