Imagine a Venn diagram. If set A equals Mad Science, set B equals Victorian Detectives and Intrepid Reporters, set C equals Gender Swapping and Social Commentary, and set D equals Lovecraftian Monsters, then The Constantine Affliction is A ∩ B ∩ C ∩ D: the intersection of awesome.

The latest alter-ego of established writer Tim Pratt, T. Aaron Payton has written a novel that spits in the eye of any attempt to pigeonhole its genre. Squint, and it looks like steampunk; turn your head and it's alt-historical science fantasy; peer from the right angle, and it resembles a story of the great detective—on meth, with monsters. Perhaps it's best to call it "gonzo-historical" in the vein of Tim Powers and K.W. Jeter—as the author himself has done—and leave it there.

London, 1864. Thirteen years after the Great Exhibition, this is a city of scientific marvels and disasters: clockwork whores, monsters in the Thames, electric omnibuses, the undying alchemical fires of Whitechapel that have been burning since the great disaster of '29. . . . Society has been riven with scandal since the first outbreak of the Constantine Affliction, a sexually transmitted disease that kills some of its victims and physically transforms others: men, changed into women's forms; women, into men's—though the law fails to recognize their transformation. Queen Victoria still holds her throne, but Prince Albert, now with a woman's body, is imprisoned in the Tower. Payton sketches in the alterations to his changed London with a deftly playful hand, and salts the text with hints and references to other works of literature. A certain Orlando, returned from Constantinople, is reputed to be the Constantine Affliction's Patient Zero; in a lab below London, the scientist Adam, Frankenstein's monster, conducts experiments in bringing the dead back to life in search of love—and meanwhile, he works on the side for a criminal boss and for a twisted visionary who wants nothing less than to "improve" the world to his own specifications.

Pembroke Halliday, Pimm to his friends, is the younger brother of a marquis. Possessed of independent means and a penchant for criminology, he relieves his boredom by excessive drinking and by consulting with the police. He's also engaged in a marriage of convenience with his best friend Freddy, one of the victims of the Constantine Affliction. Freddy, now Winifred, is still legally a man, and it would be a scandal if word got out. So when notorious criminal Abel Value needs a man who can figure out who's killing Value's human prostitutes and leaving them on the doorsteps of his clockwork brothels, Pimm proves eminently, if reluctantly, amenable to blackmail.

Clockwork brothels are, too, central to the involvement of our second protagonist. Intrepid reporter Ellie Skyler conceals her gender behind the byline of E. Skye. In the course of researching an exposé of London's clockwork sex trade, Ellie visits a den of wind-up iniquity. There, she stumbles upon famed scientist Sir Bertram Oswald, intimate of the Queen, mucking about in clockwork guts, and only through quick thinking escapes with her life. Ellie's investigation of Sir Bertram leads her into Pimm's investigation of Abel Value's murdered whores. Together, they find themselves—and Winifred—in peril as a result of uncovering a plot to dethrone and replace Her Royal Majesty: a plot that will culminate with the summoning of Lovecraftian monsters from another dimension in the skies over Hyde Park.

The rapid pace—at points breakneck—hurtles you along. The reader is caught up in a lively train of events that hurdles minor obstacles and leaves one with no time to consider the logic of the unfolding plot. (Though rationality and physical possibility are thin on the ground here, where most other considerations have been gleefully sacrificed in order to pack in the maximum amount of fun, entertainment, and Cool Shit.) A hiccup arises when unexpected new developments are reached in this way: I for one wasn't expecting monsters from the Dungeon Dimensions, so when they arrived they hit me a little out of the blue. (Although they did produce several—to borrow the term from TV Tropes—moments of awesome.)

So much for pace, but what about character? It's hard to say that either of our protagonists achieve great depth or great growth in the course of their adventures, although they make for enjoyable reading: Pimm is a (well-executed) variant on the upper-class English detective in the mode of Lord Peter Wimsey, albeit perhaps a little too modern-minded even for gonzo Victoriana. (The most unbelievable thing in the whole book is not the mad science or the Lovecraftian monsters, but the fact that this Victorian gentleman of means and his own household maintains only a valet: you'd expect a maid-of-all-work and a cook/housekeeper at the very least.) Ellie Skyler is the epitome of Nellie Bly reporting: daring, strong-minded, and determined that her gender shouldn't prove a bar to her success. But Payton's main characters aren't penny dreadful clichés: they prove compelling even while remaining somewhat predictable.

Less predictable by far are Payton's secondary characters: Abel Value, crime boss; Adam, scientist and monster; Big Ben, who Value keeps around for his muscle but who is later a vital help to Pimm and Ellie; and the most interesting character of all, "Winifred Halliday," born Frederick, a sometime inventor and society butterfly who delighted in shocking people in his previous life, and still delights in being shocking in her new identity. Payton's skill with characterization really shines with the supporting players.

Beneath the surface of The Constantine Affliction's pulpish capers through a scientifantastical version of Dickensian London lies an interrogation of the nature and usefulness of social constructs of gender, and of the "improving" nature of progress. The Affliction's effects are everywhere in London, but society proves reluctant to abandon rigid gender distinctions and permit women a place in the public sphere. Changed men bind their breasts and employ false moustaches to preserve their social position; changed women abandon their families and take up new identities; but even as the Affliction subverts the accepted roles of man and woman, showing that gender does not define either character or capability, the actual changes remain sordid, shameful secrets: public embarrassments, if revealed.

Payton marries a delightfully lighthearted adventure romp with an appraisal of the social nature of identity, pulling the whole thing off with no small amount of style—and a satisfying conclusion, to boot. The Constantine Affliction is one of the best, most wholeheartedly enjoyable books I've read all year. I stand by my words: it really is pretty awesome.

Liz Bourke is presently reading for a postgraduate degree in Classics at Trinity College, Dublin. She has also reviewed for Ideomancer and Tor.com.