PROLOGUE

A GIRL walks home alone at night.
   It’s All Hallows’ Eve in London, and the street that stretches before her is empty, quiet except for the soft thud of her boots on the sidewalk and the rustle of autumn leaves plucked by the wind. Hazy sodium lights struggle to shift the dark.
   The girl is dressed as a witch. Cartoon-green skin, pointy hat, a fake wart on her nose. She is coming from the Electric Ballroom, where, at a Halloween concert with her housemates, she saw the boy she likes kissing a girl dressed as a sexy angel. It immediately made her regret her costume and want to go home.
    Now she slips through the gap between two buildings, past the canal-side pub she goes to with her friends in the summer. A girl sits on the other side of a window decorated with bat decals, her face smeared with blood. A couple in matching hot-pink jumpsuits are breaking up on a bench.
    The girl takes a few steps onto the footbridge that leads over the water and down onto the towpath on the other side.
    It is here, on the bridge, that she pauses. The canal beneath her is a thin snake of shallow water. On a clear day, you can see the algae-coated detritus that collects at the bottom: the bicycles, the shopping trolleys, the tires. Tonight it is black and impenetrable. If you didn’t know its depth, you might think it fathomless.
    Across the water, the bars and restaurants of Camden Market are still busy with the Halloween crowd. Men and women in costumes cluster around the spaceship-red glow of outdoor heaters, laughing, drinking mulled wine out of steaming mugs.
    Ahead, the footbridge slopes down to the towpath that winds alongside Regent’s Canal, below street level.
    The girl hovers at the edge of the dark, weighing her options.
    Usually she avoids the canal after sunset. It is unlit. It is the kind of place she has been told all her life to avoid for the simple fact that she is a girl—but tonight she is cold and drunk and sad and hungry for the leftover pad thai she knows is waiting for her in the fridge. The path by the water is the shortest, fastest route home.
    Yet something tells her not to go any farther. Perhaps it is the memory of what happened to her on another night like this one. The stranger waiting in the dark, all the warnings she had been given growing up suddenly manifesting as flesh and breath and muscle.
    Then the girl remembers the words at her wrist and runs a fingertip over the cool metal letters sunken into her skin. Words that took her a year to find. Words that mean she no longer has to fear the night or anyone who might be lurking in it.
    She crosses the bridge. She plunges down into the blackness.
    The first part of the walk is fine. The path is narrow and cobbled. The canal is bordered on both sides by converted warehouses turned into blocks of fancy flats. Light from their windows reflects on the smooth surface of the water, creating an eerie mirror world just below the real one. Houseboats sit snug against the canal’s edge, the smell of woodsmoke clinging to the air around them. A huge, fat dog sits atop one, watching her as she passes. The sounds of revelry dissolve into the distance, but there is still life here. Still people to hear her, if she were to scream.
    She crosses beneath a bridge. It is mauled with graffiti and lit with shocking blue light to discourage drug use. Combined, they make the place feel dangerous. She moves on quickly, back into the waiting shadow.
    The next stretch of the walk is worse. There are no more houseboats. There are no more fancy flats. There is no one to come to her aid. There’s more greenery along the side of the path, vines and brambles that don’t lose their foliage as the nighttimes turn to frost. She moves closer to the water, wary of attackers hidden in the creepers.
    The girl crosses under a second blue-lit bridge, and then a third that’s rancid with the stink of urine. She makes it to the base of the stairs that leap up out of the darkness and onto the brightly lit street above.
    A girl walks home alone, but not alone.
    She feels him before she sees him. There’s no sound, or movement, or smell. Just some primordial response left over in the blood from a time before humans were humans. A sudden prickle of fright in her gut. A displacement of energy that makes her gaze snap back over her shoulder and brings her footsteps to a stop.
    Her eyes find the figure immediately, standing stationary on the path. He’s a slip of shadow, nothing more. No face, no weapon, nothing to indicate that he might do her harm. Just a man.
    But she is a girl. And she is alone. And it is night. And that is enough.
    She ducks her head and takes the stairs two at a time, but tries to do it casually, the way women do when they’re afraid but trying not to look rude. She forces herself not to run. There’s no need for desperate measures. Not yet. He’s just a man on the towpath at night. It would be rude to run.
    And sometimes.
    Well.
    Sometimes, if you run, the monster chases you; this she learned the hard way.
    So she climbs, step after measured step, up, up into the light. The staircase spits her out on Gloucester Avenue, only one street from her flat. She waits under a streetlight to see if the man will follow her, but he does not. She breathes a sigh of relief and turns for home. It’s a sloe-black, moonless night. The kind that beckons demons out of the liminal world and brings them into this one, hungry to feed on the souls of the living. London is full to bursting with magic, dark and dangerous, if you know where to look . . . and she knows, now, where to look.
    A dog barks.
    The girl looks up and stifles a yelp with her hand.
    The figure from the canal is somehow standing on the sidewalk directly in front of her. Closer than he was the first time.
    The girl stops again. Stares. Her heart crashes inside her chest. She takes small, gasping breaths as she tries to understand the logistics of what has just happened. How could he have followed her? How could he have overtaken her? How could he have moved so quickly? There’s no way. There’s no way.
    Then she remembers the words at her wrist.
    There’s no need to fear anymore.
    There’s heavy shadow to her right, the deep, wet shadow that trees cast in the forest. The girl moves toward it, into it, lets it devour her, and—
    She steps from a bank of shadows on the next street over. A little out of breath. A little frazzled. She looks around. She’s alone again. She went where the figure could not follow. Into one shadow, out of another.
    A small smile on her face now, she again heads toward her flat, only a few buildings away. The price she paid for this power—blood and money and soul—was worth it to feel safe.
    The girl climbs the five stairs up to her blue front door and unlocks it. When she steps inside and turns to close the door behind her, she finds the figure once more, now standing at the bottom of the stairs. He is unmoving and close. So very close to her now.
    It is impossible. Men cannot use magic. This is what she has been told. This is what she has been promised. Men cannot write spells. Men cannot sear invocations into their skin. Men cannot bind their souls to demons in exchange for power.
    Men cannot use magic.
    And yet. Here he is. Again.
    They stand still, staring at each other. Though—is he staring? She cannot see his face, cannot make out his eyes, his nose, his hair. He is empty space, a black hole from which no light escapes.
    The girl slams the door closed and scrambles backward. She doesn’t bother with the stairs that lead up to her flat on the third floor. She lunges into the shadowed corner of the hall, falls out of another shadow in her kitchen, then fumbles in the sink for one of the dirty knives her housemates are forever leaving to soak.
    The blade quivers like a water reed in her white-knuckled hand as she watches her front door and waits. Waits for a bang against the wood, a turning of the handle, a horror-movie moment worthy of a scream.
    It does not come.
    It does not come.
    It does not come.
    And then, when she thinks perhaps she is safe, perhaps he was no more than a Halloween prankster out for a laugh, a pair of strong hands close around her throat.