Drood, By Dan SimmonsThe Last Dickens, By Matthew Pearl

Here are three unsolved mysteries. How did Charles Dickens intend his last novel to end? Why have we recently had a outbreak of fiction inspired by it? And, perhaps strangest of all, why do we have such an enduring interest in the secrets of the Victorians?

In March 1870, Queen Victoria granted Dickens a private interview. Afterwards, he wrote to the Clerk of the Privy Council, saying that if the Queen was interested, he would give her a sneak preview of what lay in store for readers of The Mystery of Edwin Drood. Unfortunately, Victoria wasn't interested. Less than three months later Dickens suffered a fatal heart attack.

He had written only six of the projected 12 monthly numbers. But it was already clear that the book was something of a departure for him. It was to be shorter than usual – though its projected length of nearly 200,000 words would have made it much longer than most modern novels. It was a mystery reminiscent of The Moonstone, the recent bestseller written by Dickens's friend and son-in-law Wilkie Collins. The plot turns on the disappearance and possible murder of Edwin Drood. The principal suspect is Drood's uncle, John Jasper, cathedral precentor and opium addict, who nurses a sinister passion for Edwin's former fiancée.

Since 1870, there have been several attempts to complete the novel. Drood scholarship has also flourished. One theory, put forward by Edmund Wilson among others, speculates that the novel's resolution would have turned on mesmerism and Thuggee. Dickens wrote to his biographer Forster that he had "a very curious and new idea for my new story ... a very strong one, though difficult to work." There is hearsay evidence that under pressure of serial publication Dickens had lost his way in the plot, and no longer had a very clear idea of how it would end.

None of three recent novels connected with Edwin Drood continues Dickens's story. Instead, each author uses the book as a starting-point for his own. The British edition of Jean-Pierre Ohl's Mr Dick, translated by Christine Donougher (Dedalus, £9.99), was published at the end of the last year: a wonderfully inventive story of a feud between two French Drood scholars, interposed with the unreliable journal of a young Frenchman who visits Dickens just before he dies.

Dan Simmons's Drood is less concerned with Drood the novel than Drood the man. It's narrated by Wilkie Collins himself. He is unreliable too, because chronically jealous of his far more successful friend, he consumes industrial quantities of laudanum, and is routinely haunted by his own double.

In 1865, five years to the day before his death, the real Dickens was involved in a terrible train crash in Staplehurst, Kent. To add scandal to catastrophe, he was travelling with the young actress who was probably his mistress, and the young woman's mother. In Collins's narrative, Dickens encounters the nightmarish figure of Drood preying on the survivors at the scene. Drood has a face like a skull, lidless eyes, sharpened teeth, and a foreshortened nose – "more black slits opening into the grub-white face than a proper proboscis". He turns out to be an Egyptian zombie cannibal and the bastard son of Lord Lucan (a fictional peer, apparently). A dark quest takes Collins and Dickens into a phantasmagoric "Undertown" populated by feral children and opium addicts before a climax involving the writing of Edwin Drood, mesmerism, and the fraticidal relationship between the friends.

Simmons's novel is a long, overweight gothic fantasy, stuffed with the fruits of its author's research. The fictional Dickens, Collins and their world do not quite correspond with historical reality. But the story has a manic energy that compels shock and awe, if not belief. The closer it comes to fantasy, the better it becomes.

The Last Dickens by Matthew Pearl is more straightforward. It opens just after Dickens's death, and involves the efforts of one of his American publishers to safeguard his firm's profits by discovering how Dickens planned his last novel to end. But other forces are at work, involving murder, the opium trade, the Bengal Mounted Police, and the inspiration that gave Dickens the basis for Drood. The narrative moves from India to America to England. There's also a flashback, structurally awkward but perhaps the best part, describing Dickens's successful American lecture tour in 1867. It gives a vivid picture of Dickens as an international superstar, a cross between J K Rowling and John Lennon, hemmed in to the point of paranoia by his celebrity.

Pearl's research, like Simmons's, is often impressive, but he doesn't have a convincing sense of British contexts, or much of an ear for British idiom. There's a less than plausible portrait of Frederic Chapman, Dickens's London publisher, who uses an almost wilfully American interjection, "Say", and speaks in a sub-Wodehousian lingo.

Barring a literary miracle such as the discovery of Dickens's notes, we shall never know how he planned to resolve The Mystery of Edwin Drood. But it isn't surprising that three very different authors should write novels that reflect on the subject. Some authors, from Shakespeare to Woolf, via Austen and Poe, acquire a status that lends itself to fictional exploitation. Dickens is exceptionally well-endowed in this respect, not least because his last novel was an unfinished mystery and so, in a sense, were aspects of his own life. In all three novels, the mystery of Edwin Drood becomes to a large extent the mystery of Charles Dickens.

But there is another, wider influence at work. These fictional tributes to Dickens also point to our continuing fascination with the Victorian period, in fact and fiction. The evidence is ready to hand, for the Victorians documented their world with a thoroughness no previous era had achieved. The complex underworld of Victorian life has never been entirely concealed from view, but more of its machinery has become easily accessible in the last 30-odd years.

The Victorians traditionally stand for sobriety, thrift, hard work, the sanctity of the family, strict sexual morality, social convention, and unquestioning respect for authority, secular and religious – all qualities, perhaps, that many of us feel our society lacks. What we really enjoy are glimpses of the darker characteristics that underpinned the publicly proclaimed virtues of our 19th-century forbears. There, of course, lies the heart of the mystery, the reason for our interest: this is the world that made our own; these are the people who made ourselves.

Andrew Taylor's latest novel is 'Bleeding Heart Square' (Penguin)

Dickens's last years

Following his separation from his wife and his affair with young Nelly Ternan, Dickens's writing began to stumble. On 9 June 1865, he and Nelly were on the train that crashed at Staplehurst, killing 10. He rescued many survivors – and the manuscript for 'Our Mutual Friend'. He never really recovered from the accident, but toured Britain and America against the advice of his doctor. He died, five years exact-ly from the day of the crash, having half-written 'Edwin Drood'. He is buried at Westminster Abbey.