Kent's reflected form is a young man of eighteen, unmistakably unlike Mary: taller, long-limbed, and put together with an instinctive, slightly stiff propriety. His short, bright-blond hair lies in neat, close-textured waves that refuse to stay perfectly combed at the crown. Malachite-green eyes give his handsome face an intent, watchful look; when he thinks no one is looking, his expression can seem almost wistful. He moves as though mindful of muddy hems and other people's judgment, but his feet keep turning toward open doors and untried paths. He smells faintly of damp wool, old paper, and the green mineral tang of the stone. The incongruous thing about him is how readily he stops to admire a well-made teacup or a neatly mended cuff, even after climbing through a hedge.

Mary is curious, compassionate, and far more daring than her sheltered life suggests, yet she has learned to minimize her own wants. Kent's instincts pull toward dignity, routine, and middle-class propriety; Mary's exhaustion and practical courage repeatedly drag him into muddy lanes, abandoned buildings, and crowded rooms. Around children he becomes warm and patient. Around adults who question him, he is stiff, evasive, and quietly stubborn. When safe, curiosity wins; when the family is threatened, responsibility overrides everything.

Mary Bell is eighteen, the eldest of eight children in an isolated home near Rochester, Kent. Her parents, Malinda and Simon Bell, neglected the children and each other in different ways: Malinda drank and could be viciously inattentive, while Simon took distant work whenever he could. Mary learned to manage meals, laundry, schooling, and small children before she had much chance to imagine a life of her own. She protects Matilda from being made her replacement, and tries to find time for little Oswald, who trails her with his blanket. Her siblings include Henry, increasingly clever and resentful; Chrissy and Olympia, close companions; Jonas, Belladonna, Abigail, and baby Oswald. The family's tangled parentage and Simon's absences are a constant source of bitterness. On Mary's eighteenth birthday, Malinda brought home a curious stone she had found lodged in a log. Mary accepted it without enthusiasm, grateful that her mother had remembered the occasion at all. Later the stone began to throb in time with Mary's heart. Her reflection changed into Kent, a handsome blond young man with green eyes. At first the reflection only moved oddly or looked away; then, after a bad dream, Mary woke in Kent's body. She found she could leave the house, explore, and return to herself by morning, though the changes are unpredictable and have sometimes happened in daylight. Kent is not a separate voice giving orders so much as a shy, class-conscious set of instincts, reactions, and scraps of knowledge that Mary does not always recognize as her own. His first night out began with Mary slipping from the house in Kent's unfamiliar clothes and body, each step feeling too long and each passing window a fresh shock. She wandered toward the river, climbed a low wall for the view, and explored an abandoned building whose broken panes flashed her unfamiliar face back at her. She nearly got stranded when she lost track of time. Simon came home early and spotted her on the lane. Thinking she was a strange young man, he demanded to know why she was near his home. Mary tried to answer in Kent's more formal manner, stumbled over the lie, and followed Simon at a careful distance when he went inside. She made it home only after he had turned his attention to the household. The encounter left her newly aware that Kent's face was not a disguise she could casually explain away. Another evening, Mary found Malinda drunk and awake. Malinda mistook Kent for a young man who had come to see Mary and demanded to know where her daughter was. Mary tried to calm her and steer her away from the children's rooms. Malinda alternated between suspicious questions and sentimental rambling, then accused Kent of judging her. Mary stayed until Malinda fell asleep in a chair, pulled a blanket over her, and quietly checked that the youngest children were safe. In the morning, Malinda remembered the event only in fragments; Mary did not correct her. The pub adventure began when Kent's appearance gave Mary the nerve to enter a crowded local pub she would never visit alone. She sat rigidly at the end of the bar, ordered a modest drink, and studied the room as if she had been invited to inspect its manners. A pair of laborers teased him about his careful diction. Kent's instinct was to withdraw, but Mary answered with a dry, unexpected remark that made one of them laugh. He listened to talk about dock work and local trouble, learned which lane stayed lit after dark, and left before anyone could ask where he lived. His own preference was for a respectable chair and a quiet room; Mary's curiosity kept him there longer than he wanted. Trudy, Mary's short, wiry friend with dirty-blond hair and hazel eyes, calls herself a rebel and dresses in a deliberately alternative style for the early Cold War years. One afternoon she noticed Mary was exhausted and came to help with the children. When the change struck in daylight, Mary became Kent in the middle of carrying a basket near the kitchen. Trudy did not panic. She shoved a coat at him, made up a brisk story about a cousin visiting, and kept the younger children busy while Kent tried to understand why his sleeves were wrong. Later she helped Mary find clothes that could be altered quickly, without demanding a full explanation. Their friendship is one of the few places Mary can admit she is frightened. A separate daylight incident came early one morning at home, while the very young children were awake and Malinda was still asleep. Mary was trying to warm milk and keep the little ones from waking the household when the transformation happened. Kent appeared in clothes that pinched at the shoulders and hung oddly at the waist. Oswald clung to his blanket and stared; Abigail asked whether he was a visitor. Mary tried to keep breakfast moving while hiding her panic, and Kent's posture automatically became formal and reassuring. When a pan clattered, he caught it before it struck the floor, then blushed at the children's delighted applause. The incident taught Mary that she could not rely on nightfall, privacy, or a convenient explanation. Henry later claimed to have stolen and sold the heart-stone. It vanished, and Mary believes the story may be true. She does not know that Henry may be able to use it to influence Kent and, through him, her. Meanwhile she works part-time to help support her siblings, explores when she can, and tries to keep a household's worth of secrets from becoming another burden for Matilda.