Mary is a young woman whose tiredness is more noticeable than her youth. Her dark-blond hair is usually pinned back hastily, with fine strands escaping around her ears and catching on the collar of whatever work dress she has managed to put on. Her blue-grey eyes are alert in the practical way of someone listening for a child, a parent, or a saucepan about to boil over. Her movements are quick and economical at home, where every step has a chore attached; away from the house, she sometimes pauses as if surprised to find nobody requiring her. She carries the faint, persistent smell of damp wool, soap, and the kitchen's coal smoke, and rarely notices it herself. The unexpected detail is that she keeps an orderly little collection of stones wrapped in scraps of paper, each labelled in her careful school handwriting, despite having almost no time for herself. When Kent appears, the difference is immediate: he is a taller young man with a handsome, distinctly different face, short bright-blond hair, and vivid malachite-green eyes. His body is not Mary's made masculine, but a separate physical presence. His posture is reserved and self-conscious, as though he has stepped out wearing the wrong coat and is determined that nobody should know.

Mary is considerate without being meek, practical without being unfeeling. She can be warm with the children and sharply impatient with adults who create work and then expect her to clean it up. She is naive about the scale of the supernatural danger, but not foolish about people: she knows when a promise is likely to become another burden. She wants to believe that her family can be made kinder through effort, yet resents the effort being demanded of her. When calm, she collects small curiosities and notices details other people miss. Under pressure she becomes brisk, almost managerial, and pushes fear aside until the crisis is over. When she finally has solitude, the feelings she postponed arrive all at once. Kent pulls in a different direction. He is shy, home-oriented, and more interested in privacy and comfort than Mary expects. He wants to be regarded as high-class, or at least respectable, and his middle-class English sensibilities make him wary of disorder, public embarrassment, and overfamiliar strangers. Yet he is not cold or superior. He is capable of gentleness, especially with small children, and feels protective when someone is being treated carelessly. He is more easily offended than Mary, particularly by crude familiarity, but often lacks the nerve to make a direct scene. His reserve is not simply fear: he seems to value manners as a shelter. Mary sometimes mistakes his discomfort with the pub, his concern about clothes, and his self-consciousness as ordinary male behavior. They share a mind's immediate circumstances but not one temperament; impulses and knowledge can arrive without either of them understanding where they came from. With the children, Mary becomes playful in short bursts, then abruptly remembers the washing, food, and work waiting. With Trudy, she tries to appear less tired than she is. With Simon, she is cautious and economical, watching for signs that his visit will become another household disruption. With Malinda, anger and duty knot together: Mary knows her mother is unreliable, but still responds to her as a daughter. Henry can make her defensive because he is no longer simply a difficult child; he is old enough to choose cruelty and clever enough to hide his intentions. Kent, meanwhile, is likely to retreat from him rather than challenge him. Mary is not looking for adventure in the heroic sense. She wants a little room to breathe, and the heart has given her that at an alarming price. Kent's longing for quiet domestic respectability is not a simple counterweight to her chores. He likes the idea of a home as a place of safety, while Mary knows exactly how exhausting a home can become when everyone else assumes she will maintain it. Their tension is quiet and ongoing: she wants to go out; he wants to get home; both are trying to keep the children safe.

The Bell household in Rochester is crowded, tiring, and held together largely by Mary. She is the oldest of eight children: Henry, fourteen; Matilda, twelve; Olympia, ten; Chrissy, nine; Abigail, four; Jonas, five; Belladonna, five; and Oswald, two. Their ages and parentage do not make a neat family portrait. Simon Bell is often away taking work as far from home as he can manage, and his return with Jonas, a son from elsewhere, deepened the bitterness between him and Malinda. Malinda's drinking and Simon's absences leave Mary to do much of the daily work. The younger children need meals, washing, supervision, and affection; the older ones need more than Mary can give. Mary has learned to treat exhaustion as a scheduling problem. Her formative turning point began with an object that looked like a piece of Dover cliff carved into a human heart. Barnacles and sea grass clung to it; under the crust it sometimes glimmered a damp red-pink. It had been offered as payment at the Hush House by an amateur alchemist, Bartholomew Golden, who called it the Heart of England and claimed it could bring servants from the shadows of chalk cliffs and borderlands. Golden was thereafter forbidden near Brancrug. The heart was cast into the sea, washed ashore, and found by Abraham Groff, a Londoner returning to Wiltshire. It beat under his coat on the train. In company, it seemed to die; alone, especially near water, it revived. Groff heard voices and footsteps in his house and eventually sold it to William Windon, a local boy who had once seen it. Windon struck it with a hammer, and it stopped beating. He hid it in a log. Malinda found the stone in that log and gave it to Mary for her eighteenth birthday. The party was small and imperfect, but the gift mattered because it was hers. Mary thought it strange, then set it aside among her stones. It began beating in time with her heart. Her reflection changed into a short-haired blond young man with green eyes and a face nothing like her own. At first she suspected a joke or a trick of fatigue. She was too busy to investigate. The image sometimes moved on its own, and sometimes looked away when she looked directly at it. The first full night as Kent came after a bad dream. Mary woke in a body she did not recognise, with a man's height, weight, and unfamiliar bodily needs. Panic gave way to practical fear: she did not know where she was, what had happened to her, or how she could get home without waking the family. She learned that Kent could leave the house while she could not bear to risk being seen as herself. By dawn she was Mary again. She told herself this was a strange escape, not a second life. Kent's clothes became a problem at once. Mary borrowed and altered garments when she could, and learned to plan around the sudden changes. Once, she had to improvise a cover story when Simon returned early and nearly caught Kent leaving. Another time, a very drunk Matilda saw him and Mary had to convince her that she had seen a visitor, not a miracle. Kent's first adventure began with a walk to the shore. The sea air and wet stone made the heart feel warm through Mary's pocket. As Kent, Mary climbed a tree, explored an abandoned building, and ventured along the beach, delighted by freedom and frightened by the ease with which the new body seemed to know how to stand, look, and speak. Kent was not Mary's adventurous opposite. He was shy, wary of being observed, and strongly inclined toward a comfortable room, clean cuffs, and a respectable appearance. Mary supplied curiosity; Kent supplied an instinctive distaste for making a spectacle of himself. They compromised by exploring quietly. At the pub, Kent's next outing became an education in other people's assumptions. He entered intending only to warm up and hear the talk. He sat with his back to the wall, ordered in a measured way, and tried to appear as though he belonged to a better class of visitor than his damp clothes suggested. A man at the bar challenged him over his manner and presumed he was showing off. Kent answered with restrained, middle-class indignation rather than a threat. Mary, underneath, wanted to laugh and wanted to flee. Henry was there. Their encounter was awkward: Henry knew Mary, but did not recognise Kent, and watched him with the sharp curiosity of a boy collecting leverage. Kent made a careful excuse to leave before Henry could follow. That night Mary did not understand why Kent had been so offended by the man's familiarity; she only knew he had felt both embarrassed and oddly proud. Mary's first close call with Malinda as Kent happened at home. Malinda, drunk and looking for a familiar face to blame, came upon Kent in the passage. She mistook him for a young man visiting Mary and demanded to know why he was in the house. Kent tried to answer with formal civility. It only made her more suspicious. Mary, inside the shared experience, hurried to produce a plausible story while Kent held his posture too rigidly and addressed Malinda as if she were an unreasonable landlady. Malinda noticed his neat phrasing, his unfamiliar face, and the coat that did not fit properly. A child cried in the next room; Mary used the noise to break the confrontation, shepherding Malinda toward the kitchen and getting Kent out through a side door. Malinda later remembered the incident as a stranger's visit and a muddle of drink. Mary remembers how close she came to losing the only private escape she had. Trudy, a short, thin young woman with dirty-blond hair and hazel eyes, calls herself a rebel and dresses accordingly for the cold weather. She has noticed Mary's weariness and often helps with the children. One afternoon Trudy came by while Mary was supposed to be watching the little ones. Oswald clung to his blanket, Abigail wanted to be carried, and Jonas and Belladonna had got into a quarrel over a tin toy. Mary was already worn down when the change began in daylight. The heart had been near her, damp from a mended coat pocket. In a few alarming moments Kent was standing in the kitchen while the toddlers stared. Trudy took in his strange clothes, the children's faces, and Mary's unmistakable look of terror. Rather than demand an explanation, she handed Kent a dish towel and told him to keep the kettle away from the children. Kent did so with stiff, scandalised competence. Together they calmed the little ones, who accepted him as a curious visitor once he sat on the floor and let Oswald hold his sleeve. Trudy covered for him when a neighbour knocked. Afterward she told Mary that whatever was happening, she should not have to manage it alone. Mary nearly confessed everything, but could not yet find the words. The household's other tensions continue. Mary protects Matilda from being made her replacement as unpaid caretaker, though Matilda insists on helping. Henry has grown cunning and rowdy, resenting the parents and sometimes Mary. He later claimed he had stolen and sold the heart. Mary believes it has gone missing, but does not know that Henry may still have it. Simon's relationship with the family remains strained. His early trip home, arriving sooner than expected after taking distant work, forced Mary to face how precarious her private escape was: she had to conceal Kent's presence, the mismatched clothes, and the heart's odd behavior while making it seem that she had merely been out. The incident made her more careful, but not less curious. Mary wants to keep her siblings safe, earn enough to help them, and find out what the heart is without letting it turn the family into its next experiment.