In Welsh's exhilarating Victorian murder-mystery set in 1882 Edinburgh, Sarah Gilchrist cuts her teeth as one of the first female medical students at the city’s exclusive university. By day, Sarah dissects corpses. At night, she travels to the poor, often overcrowded slum of Cowgate. There in the dingy, malodorous surroundings, she helps attend to Edinburgh’s many “unfortunates.” Sarah volunteers at the Saint Giles’s Infirmary for Women and Children, a private clinic primarily run by the indefatigable Fiona Leadbetter, who caught the eye of Sarah’s Uncle Hugh--who in turn wanted to acquire some charitable work for his niece in the hope that he could diminish her interest in medicine.

Almost everyone, including Uncle Hugh and Aunt Emily, view Sarah with distain or suspicion: she’s just one more of the many “immoral witches” bent on a career in medicine. Aunt Emily in particular resents that Sarah has abandoned her mother’s plans of marriage, motherhood, and good social standing: “She disliked my clothes, my morals, and most certainly my choice of profession.” In this time and place, Sarah’s reputation must be kept intact, though she's already irrevocably damaged, barely separated from the prostitutes, the “wretched creatures” who haunt the streets of Cowgate.

Descending deep into Saint Giles’ dark underbelly of crime and prostitution, Sarah (“this posh girl playing in the slums”) meets Lucy Collins, a fragile creature and “a fallen woman” with opiates “in her person” and the stench of sex on her skin and in her hair. Adamant that she cannot afford to feed a child, Lucy begs Fiona to give her an abortion. No respectable doctor would collude in such a practice. Fiona balks at Lucy’s plea, and Lucy finds herself in an impossible situation, searching for a way to rid herself of the “unwanted burden.” Faced with no good options, she threatens to go to those “who are ten a penny” in an area heavily populated with brothels. Fiona tells Sarah that Lucy is one of Ruby McAllister’s girls; that whorehouse is just one of a handful that have entrusted their wretched workforce into Fiona’s care.

Back at the University, Sarah so far remains oblivious to Lucy's fate--that is until she’s about to undergo a dissection and sees Lucy’s bruised, strangled, lifeless body lying on the table. Unable to complete her work from grief over a girl she barely knew, Sarah desperately tries to uncover why someone would have had done this and why so many people failed to care. Although the police concede that Lucy suicided by taking an overdose of laudanum, Sarah--sensing a series of connections--is positive that Lucy was murdered.

Through Sarah’s radical first-person perspective, we see the perils of speaking out in a society where oppression of women is commonplace and the prejudices of men cast long shadows through the dirt of Cowgate and the more salubrious suburbs of New Town. At first, Sarah has no idea what her next step will be, other than trying to make sense of Lucy’s death. She spends much of her time prowling about, attempting to discover Cowgate’s strange new world whose rules she can barely comprehend. In the interim, she turns to Professor Gregory Merchiston, determined to investigate his possible links to Lucy. Sarah is discomfited by Merchiston’s charmless, sarcastic manner. A man who likes to fight half-naked in a room full of whores and criminals, perhaps Merchiston knows more about Lucy’s death than he’s initially letting on.

Plunging into Lucy’s investigation with a passion rare for a woman of her class and station, Sarah is hijacked by her position. Her family see her as a woman of “unclean virtue” and a taint on their privileged status in civilized society. Her female colleagues offer little support, particularly Julia Latmyer, who runs the University’s wretched Temperance League and who mocks and vilifies Sarah at every turn. Sarah finds solace with her friend, the elegant and refined Elisabeth Chalmers, who plies Sarah with tea and cake while acting as a sounding board to Sarah’s frustrations at trying to make a go of it in a world so dominated by men.

Welsh combines her murder mystery with an unusually savage indictment of a period when men ran roughshod over women, who were considered too delicate for anything other than marriage and childbirth. Sarah proves to be a good girl with a kind heart. Her journey into Lucy’s world changes her. She is transformed into an early feminist proto-warrior working to expose the cruelty and horror of Cowgate where some of the most fragile, desperate women scrabble for an existence, forced though an endless labyrinth of male degradation and gratification.