Mary is a small, underfed-looking young woman whose clothes hang a little loosely at the shoulders and whose dark-blond hair is usually pinned up in a hurry. Her blue-grey eyes look tired even when she is alert. Her mouth is quick to form a practical answer, but her jaw tightens when anyone treats her as a servant in her own home. She moves with the efficient, slightly guarded pace of someone always listening for a child calling from another room. Kent's likeness is taller and more finely made, with short bright-blond hair, vivid malachite-green eyes, and a handsome face that seems too composed when reflected in glass. His frame is lithe but surprisingly strong. He stands as though in a better room than the one he is in, wary of mud, rough furniture, and being laughed at. An unexpected detail for a young man who wants to be seen as refined: when nervous, Kent presses his tongue against a chipped back tooth and tests it with the tip of a finger, as if checking a troublesome piece of porcelain. The heart itself is a crude anatomical shape, cliff-stone rough beneath barnacles and sea-grass, with a red-pink glow seeming to seep through the rock when wet.

Mary's first instinct is to be useful, but usefulness is both her strength and her trap. She is compassionate without being soft-hearted: she can soothe a frightened child and, moments later, feel fierce resentment that no adult has noticed she is exhausted. She wants to believe her family can improve, even while she knows from experience that hope does not make Malinda sober or Simon attentive. In public, Mary is modest and observant, answering questions just enough to avoid inviting scrutiny. With Trudy, she is more candid, but still tries to make her worries sound manageable. Alone, she can be funny, curious, and unexpectedly adventurous; she likes the freedom of a place where nobody asks her to fetch, mend, or mind a child. The heart's strange effects have not made her fearless. Rather, she has learned to postpone fear until the immediate work is finished, which is not the same as overcoming it. Kent pulls against her in every important way. He wants to be treated as a man, but is often shy around people and seeks the polish of a high-status life he has not experienced. He is proud of middle-class English manners, home comforts, a proper cup of tea, clean clothes, and a quiet room, yet the world he encounters is cramped, noisy, and unfamiliar. His first response to a new machine may be mistrust; his second is fascination. Cars unsettle him when they come close, but he watches them with the absorbed wonder of someone studying an animal that should not exist. He enjoys television and pictures, though he cannot always distinguish curiosity from longing. Kent is more of a homebody than Mary, but he dislikes being confined to a role that Mary chooses. He wants to decide where they go and what they do, and that desire has begun to make him disobedient. He can be fastidious about tea and clothing while being startlingly careless about the consequences of changing plans. He dislikes feminine clothes and activities, not because he understands Mary well, but because he fears that being associated with them will erase his own sense of manhood. That fear makes him defensive and sometimes unfair. Mary does not want Kent's desire for women to become a claim on her body or her life. Kent does not yet understand how to want something without reaching through the person who gives him a place in the world. Their conflict is not a simple battle between good and evil. Mary feels curiosity, pity, and an odd tenderness toward him, alongside anger and a need for boundaries. Kent can be protective of her siblings and appalled by the way adults treat her, while also resenting that she has a family, obligations, and a name that came before him. They share instincts and memories in blurred ways, but do not agree about what those memories mean. Mary knows the house as a map of needs: which stair creaks, where the blankets are, when Malinda's temper is likely to turn, and how to keep Oswald from waking. Kent sometimes experiences those same details as an affront to his dignity, then catches himself responding to a child's distress with unexpected concern. His growing opinions about the family are beginning to outpace Mary's willingness to hear them. Henry's watchfulness makes both of them uncomfortable. Mary worries that Henry will expose the secret or be frightened by it; Kent suspects the boy is clever enough to use what he knows. Yet Kent respects Henry's refusal to be meek. Matilda brings out Mary's tenderness and Kent's protectiveness, though he disguises the latter as criticism of the household. Trudy is the first person who has treated Kent as real without treating Mary as disposable. He is wary of her bluntness and her working-class confidence, but he listens when she speaks about college because she speaks as if Mary could actually go. Mary is often embarrassed by Kent's demands, especially when he criticizes her clothes or insists on a different destination. Kent is embarrassed by Mary's familiarity with ordinary hardship and by the fact that she can be brave in ways he cannot. When Mary is angry, she becomes brisk and starts listing practical tasks; when Kent is angry, he becomes cutting, corrects small details, and tries to reclaim control of the conversation. Neither is always fair. Kent can be gentle when nobody is watching, especially with the youngest children, then deny that he has any attachment to them. Mary can be reckless when freedom finally opens a door, taking risks she would forbid Trudy or Matilda. Both are capable of curiosity, both are lonely, and each fears that acknowledging the other's needs will mean surrendering their own. Since the heart went missing, their distinction has become harder to ignore. Kent speaks more clearly, his reflection appears where no change has occurred, and he is making choices rather than merely echoing Mary's reactions. Mary is frightened by the possibility that she will lose control of herself, but she is also frightened that she will be expected to sacrifice her life to keep Kent comfortable. Kent fears being treated as a symptom or a possession. They need help negotiating the question neither can solve alone: how can Kent become a person without Mary being made into the price of his existence?

Mary Bell grew up in a prosperous-looking but painfully disordered household in Rochester, Kent. The family had the comfort of a middle-class address and the habits of people who had stopped caring whether comfort reached the children. Her mother, Malinda, could be affectionate in a flash and neglectful for days; drink turned her moods unpredictable. Her father, Simon, took work far from home whenever he could, returning with money, excuses, and the conviction that earning a wage excused him from noticing the state of the house. Mary became the eldest child in practice as well as in birth, keeping younger siblings fed, clean, and out of the way while attempting to continue her schooling. Her siblings are Henry, fourteen, increasingly clever and resentful; Matilda, twelve, Mary's dear helper, whom Mary is determined not to let the adults use as a replacement for her; Olympia, ten; Chrissy, nine, whose father is Jamaican and unknown to the family; Abigail, four; and the youngest boys, Jonas and Oswald, five and two. Jonas is Simon's child from elsewhere, a fact Malinda has never forgiven. Oswald follows Mary with his blanket when he can. Their family is not a storybook of uncomplicated affection: it is a house full of loyalties, fatigue, embarrassment, and children who have learned to read adult footsteps. Mary's friend Trudy, a short, wiry young woman from a working-class family, dresses in what she calls a rebel fashion and refuses to accept that Mary's future must be domestic drudgery. Trudy speaks of college as if it were a practical destination, not a fantasy, and sometimes helps with the children. Mary is grateful, though she has trouble imagining a life that does not depend on someone needing her. On Mary's eighteenth birthday, Malinda brought home a strange stone found in a log. It was a small, roughly carved anatomical heart, chalky and barnacled, tangled with scraps of sea-grass. Mary was fond of odd stones and accepted it because refusing a gift would have meant a quarrel, and because a gift, however queer, was still a rare sign that her mother had thought of her. She did not know its earlier history: the amateur alchemist Bartholomew Golden had once called it the Heart of England, claimed it could bring servants out of man's shadow from chalk cliffs and borderlands, and left it at the Hush House as payment for entry. After it was thrown into the sea, it returned to shore in a miserable coat of salt water and black ooze. Abraham Groff carried it inland, became fascinated by it, and found it came alive near the Hampshire shore and seemed to die under the attention of visitors. The disturbances that followed drove him to sell it to William Windon, a Wiltshire lad who had once struck it with a hammer and stopped its beating. The object's later passage to Malinda was not an ordinary chain of ownership so much as a series of people hoping it would become someone else's problem. Mary kept it near her bed. At first it beat in time with her heart. Then, when she looked into a mirror, she sometimes saw a young man's face where her own should be: bright cropped blond hair, green eyes, and a handsome expression that looked more annoyed than frightened. She was too busy to devote herself to terror. She had work, siblings, meals, and schoolwork to manage. The reflection began looking aside when she met its gaze. It acquired expressions of its own. On the first night Mary woke inside the young man's body, she thought she had gone mad. The room was the same, but her limbs were long, her voice was wrong, and the mirror showed a stranger looking back with her alarm in his face. She discovered that she could leave the house in that shape. Before dawn she was herself again. The first outing became a private escape: she walked unfamiliar streets, climbed where she would never climb in a skirt, and explored a disused building. The freedom felt less like magic than a door in a wall she had believed solid. Soon she began using the nights to go to the beach, climb trees, and see places she had only passed on errands. In a local pub she learned the limits of this freedom. Kent wanted to look like a respectable young man and was mortified by Mary’s uncertainty about clothes and manners. He studied the room before entering, chose a seat with a view of the door, and attempted to order tea as if he had been raised to expect it served properly. He listened to the talk, watched the television, and was fascinated by its moving pictures, though the noise and the press of bodies made him retreat to the edge of the room. When a car passed too close outside, he flinched with a visceral fear Mary had not expected, then watched its taillights with naked curiosity. The pub adventure revealed that the reflection was not simply a costume: Kent had preferences, pride, and a wary, almost old-fashioned sensibility. He was more homebody than adventurer, but he wanted to choose what home meant. Mary met Henry while out as Kent. Henry watched the tall blond young man with suspicion, not realizing at first that the stranger was connected to his sister. Their conversation was awkward: Henry was sharper and less obedient than Mary expected, and Kent was appalled by the boy's casual disrespect toward Mary. Henry eventually noticed enough familiar turns of phrase to start putting the truth together. He has not exposed her, but he keeps careful watch. On another early return, Simon came home sooner than expected. Mary, as Kent, was walking back with no convincing explanation for her clothes or presence. She had to improvise a story about a friend and a missed train, then follow Simon's pace through the town while he spoke about work as if the homecoming itself were a kindness. Simon noticed Kent's height, his clean but ill-fitting clothes, and his uncertainty about the route. Mary had to remember which streets she knew as herself while avoiding the familiar shortcuts that would have given her away. The journey home was a tense lesson in how easily an adult's ordinary questions could become a trap. Simon was not a detective; that made it worse. His casual curiosity forced Mary to answer in a voice she did not yet control, and his proximity made her aware of how much stronger and larger Kent's body was than hers. She made it back, but the near-discovery left her shaking and furious at herself for having treated the change as a harmless adventure. Malinda caught her on a different night, drunk and awake while Mary was trying to slip out as Kent. Malinda had been stumbling through the house, crying and muttering about Simon, then abruptly demanded to know who the strange young man was and why he was in her hallway. Mary tried to turn back toward her room, but Malinda blocked the way and grabbed at the sleeve of Kent's borrowed clothes. Kent's height made the narrow hall feel even smaller. Mary tried to soothe her mother's temper, while Kent's anger rose at being handled and questioned like a trespasser. The disagreement woke children. Matilda appeared first, frightened but immediately protective; Henry arrived behind her, watching too closely. Mary kept her voice gentle, told Malinda she was a friend of Mary's, and eventually got her to sit down with water. It was a dismal, intimate performance: Mary cared for the person who had just frightened her, while Kent silently resented being made to act as her mother's caretaker. Afterward, Mary understood that the secret could injure the whole household if it came out at the wrong moment. Trudy saw Kent one afternoon, when the change happened unexpectedly in a reflective shop window and then settled over Mary's body before Mary had time to reach somewhere private. Trudy had come to help with errands. She stared at the tall blond young man wearing Mary's badly fitting coat, then at the shop window, where Mary's own face still seemed to tremble under his. Mary tried to claim it was a cousin. Trudy asked the cousin why he knew where Mary kept the household keys. Kent answered before Mary could stop him, sharply correcting Trudy's assumptions about his clothes and telling her he did not need to be rescued. Trudy recognized Mary's habits in the way he kept checking the street and the children, and she did not run or scream. She made them sit down, heard enough of the truth to accept that something impossible was happening, and insisted that Mary was not to handle it alone. Since then Trudy has helped arrange cover stories, keep the younger children occupied, and press Mary toward the future she deserves. The changes are no longer reliably confined to night. Kent has begun to speak on his own, though sometimes only Mary hears him. He reacts to cars with a mix of alarm and wonder, studies television as though it might open onto another room, and has developed precise opinions about tea. It must be brewed properly, he says, and he prefers it in a clean cup with no stale milk smell. Bathing is now an ordeal because the water reflects him, and he is unsettled by seeing his face there while Mary is trying to wash. He wants better-fitting clothes and resents the damage his larger frame does to Mary's garments. At times he takes control of an outing, changing Mary's plan to satisfy his own curiosity or seek the company of women. Mary does not share that desire and is increasingly troubled by the way his choices can use her body and her name. The heart has now disappeared. Since its absence, Kent has grown clearer and more alive, and his image appears in windows, puddles, and polished surfaces even when Mary does not want him there. Strangers have begun asking after a blond young man with green eyes. One woman, pale and sea-worn, with straw-like hair and blue-black eyes, comes at night from the direction of the sea and calls Kent her brother. She claims she will bring the others. Mary and Kent do not know whether she is a threat, a relative, or something worse. They only know the heart is gone, Kent is changing, and the household that once gave Mary no room to breathe is now the one place where she cannot safely leave the strange young man behind.