Five years later.

The tires of the Gulfstream private jet screech against the tarmac of JFK International Airport.

Katerina steps down the stairs, the sharp click of her black stilettos echoing in the crisp morning air. She wears a tailored black suit that hugs her slender frame. Her hair is pulled back into a severe, flawless bun.

She is no longer the pathetic, discarded wife. She is Astrid. The ghost. The medical fixer for the global elite.

Elie Mcdonald stands by a waiting armored SUV. He hands her an encrypted tablet as she slides into the leather backseat.

"Your VIP patient," Elie says, closing the door.

Katerina swipes through the medical file. The name is redacted. The symptoms are severe: chronic migraines, insomnia, violent mood swings. The patient has fired-and physically thrown out-five neurologists in the past month.

The SUV pulls into the underground garage of a highly discreet private clinic on the Upper East Side.

Alistair Crombie, the clinic director, is sweating through his suit as he waits by the private elevator.

Katerina steps out. She reaches into her bag and pulls out a sleek, silver half-mask. She secures it over her face, leaving only her eyes and lips exposed.

"Dr. Astrid," Alistair stammers, pressing the button for the penthouse floor. "Please be careful. He is in a terrible mood today."

The elevator doors open. The hallway is lined with men in dark suits.

Katerina's eyes narrow behind the mask. The cut of the suits, the specific way the men stand with their hands clasped in front of them-it tugs at a dark corner of her memory.

She ignores the rising dread in her stomach and walks to the heavy mahogany double doors at the end of the hall. Alistair pushes them open for her and quickly steps back.

The VIP suite is suffocatingly dark. Heavy blackout curtains block out the Manhattan skyline.

A tall, broad-shouldered man stands by the window, his back to the door. Smoke from a cigar curls around his dark hair.

Katerina steps onto the thick carpet, her medical case heavy in her hand.

Hearing her heels, the man turns around.

The dim light from a wall sconce catches the sharp angles of his jaw, the straight line of his nose, and those amber eyes.

Katerina's lungs seize. Her heart slams against her ribs so hard she feels it in her throat.

Cayden Merritt.

He looks older. Harsher. The lines around his mouth are carved deeper, and there is a dark, dangerous exhaustion in his eyes.

Cayden crushes the cigar into an ashtray. His gaze sweeps over her, sharp as a scalpel.

"You're the miracle worker everyone is terrified of?" His voice is a low, gravelly rasp.

Katerina grips the handle of her medical case until her knuckles turn white. The leather digs into her palm. She forces her breathing to slow. She cannot panic.

"Yes," she says. She alters the placement of her tongue, producing a clipped, cold, faintly European accent.

Cayden takes a step toward her. Then another. The sheer physical dominance of the man fills the room, pressing down on her chest.

He stops less than two feet away. He looks down at her, his eyes locking onto hers through the eyeholes of the silver mask.

A slight frown creases his forehead. His amber eyes darken with a sudden, restless confusion. Something in her gaze is scratching at his subconscious.

Without a word of warning, Cayden raises his hand, his long fingers reaching straight for the edge of her silver mask.

Katerina snaps her head back, dodging his fingers by a millimeter.

She takes a swift step backward, putting distance between them. Her heart is a frantic bird trapped in her ribcage, but her eyes remain dead and professional.

"Do not touch my equipment, Mr. Merritt," she snaps, her European accent thick with icy authority. "That is a boundary you will not cross."

Cayden's hand hovers in the air for a second. He stares at her, slightly taken aback by the sheer venom in her tone.

The Katerina he knew-the woman whose ghost haunts his migraines-would have flinched and apologized. This woman is pure, arrogant steel. The fleeting sense of familiarity vanishes, replaced by irritation.

He drops his hand and sneers. "Just do your job."

He walks over to the leather recliner and sits down, leaning his head back and closing his eyes.

Katerina forces her shaking hands to open the medical case. She pulls out a set of neuro-sensor patches. The smell of his cedar cologne hits her, thick and suffocating. Her stomach rolls with a phantom wave of nausea.

She steps close to him. She reaches out to place the first patch on his temple.

Her bare fingertip accidentally brushes the skin of his forehead.

Cayden's entire body goes rigid. A violent jolt of electricity shoots through his veins. His eyes snap open.

Before Katerina can pull back, his hand shoots out. His fingers wrap around her wrist like a steel vice. His grip is bruising, desperate.

"Who are you?" he breathes, his voice tight, his amber eyes wide with a sudden, raw confusion. A flash of something wild and unfamiliar-a memory he couldn't quite grasp-crossed his face.

Katerina tries to yank her arm away, but he holds fast. "Let go of me."

Cayden opens his mouth to speak, but a piercing, high-pitched alarm shatters the silence.

It's coming from the pager in Katerina's lab coat. The emergency extraction signal from Elie.

Katerina uses Cayden's momentary distraction to violently twist her wrist out of his grip. She takes two steps back, pulling the pager from her pocket.

"My critical patient in Geneva just went into cardiac arrest," she lies smoothly, her voice urgent. She throws the sensors back into the case and snaps it shut. "I have to go."

Cayden stands up, his massive frame blocking her path to the door. "You aren't leaving until I get answers."

His bodyguards step into the doorway, blocking the exit.

Katerina glares up at him. "If that patient dies because you delayed me, the International Medical Consortium will ensure you never receive medical treatment anywhere on this planet again. Move."

Cayden's jaw ticks. He is about to order his men to grab her when his private cell phone vibrates violently in his pocket.

He pulls it out. It's Simon. He answers it, his eyes never leaving Katerina's mask. "What?"

"Boss," Simon's voice is shrill, bordering on hysterical, bleeding through the phone speaker. "Julian is gone. He disappeared from the lobby."

The blood drains from Cayden's face. The mystery of the doctor evaporates instantly.

"Lock down the entire block!" Cayden roars. He shoves past Katerina, sprinting out the door, his bodyguards swarming after him.

Katerina exhales a shaky breath, sweat beading on her forehead. She doesn't waste a second.

She slips out the door and heads for the internal staff stairwell. She strips off the white lab coat, shoving it into a trash can. She pulls off the silver mask and slides a pair of oversized black sunglasses onto her face.

She takes the stairs two at a time, heading straight for the underground VIP parking garage. She needs to get to her car. She needs to get back to Leo.

The underground VIP garage is damp and smells of exhaust and old concrete.

Katerina walks quickly, her heels clicking against the pavement. She pulls her keys from her purse, pressing the unlock button. A black SUV flashes its lights fifty yards away.

A sharp, terrified scream echoes through the cavernous space.

Katerina freezes. The sound of a child in pain bypasses her brain and strikes directly at her maternal instincts. She ducks behind a thick concrete pillar, peering into the dim light.

Near the exit ramp, a gray, unmarked van is idling. Two massive men wearing black ski masks are dragging a small boy toward the open sliding door.

The boy is kicking and thrashing. The overhead fluorescent light flickers, illuminating the side of the boy's face.

Katerina's breath stops.

The dark hair. The straight nose. The exact curve of his jaw.

It's Leo.

Her mind registers a split-second flash of something wrong-the boy is wearing a formal navy suit, not Leo's usual clothes-but the fluorescent light cuts out again, plunging the van into shadow, and she doesn't have time to think. In her mind, the men are shoving her entire world into that van.

A blinding, roaring rage erupts in her chest.

She kicks off her stilettos. Barefoot, she sprints out from behind the pillar.

One of the kidnappers is pushing the boy into the backseat. Katerina uses the hood of a parked sedan as a springboard. She launches herself into the air, her leg swinging in a brutal arc.

Her shin connects with the back of the kidnapper's neck with a sickening crunch.

The man grunts and collapses face-first onto the concrete.

The second kidnapper spins around, his eyes wide. He pulls a serrated hunting knife from his belt and lunges at her.

Katerina sidesteps the blade. She grabs his wrist with both hands, using his forward momentum to twist his arm violently behind his back. The bone pops. The knife clatters to the floor.

She drives her elbow into his throat. He drops to his knees, gasping for air, clutching his crushed windpipe.

Katerina dives into the back of the van. She grabs the terrified boy, pulling him tightly against her chest.

"Leo, Leo," she gasps, her voice breaking as she switches instinctively to Mandarin, the language she always used with her son in their most private moments. "Are you hurt? Let me look at you."

Julian is completely frozen. He stares at the beautiful, frantic woman holding him. He doesn't understand the language, and he has never, ever been hugged like this. He stays completely silent, his body stiff.

The sound of shouting and heavy boots echoes from the stairwell entrance.

Katerina assumes it's more kidnappers. She scoops Julian up, holding him tight, and sprints toward her black SUV.

She throws him into the passenger seat, slams the door, and jumps behind the wheel. The engine roars to life. She slams her foot on the gas. The SUV tires squeal, burning rubber as she smashes through the wooden exit barrier and speeds out into the Manhattan traffic.

Ten seconds later, Cayden bursts into the garage, a dozen armed men behind him.

He sees the two groaning men on the floor and the empty gray van.

"Where is he?!" Cayden bellows, grabbing a security guard by the collar.

"Camera room! Now!"

Cayden storms into the security booth. The guard scrambles to rewind the footage. The screen is grainy, the angle poor.

Cayden watches the footage. He sees a woman in black clothes and oversized sunglasses take down the two men with lethal precision. He watches her grab Julian, put him in a black SUV, and speed away.

Cayden hits the pause button. He leans in, his nose almost touching the monitor. He stares at the black tailored suit the woman is wearing.

It's the exact same suit the doctor, Astrid, was wearing under her lab coat.

Cayden's fist slams down on the glass-topped desk, the heavy surface shuddering under the violent impact.

"It was her," Cayden snarls, his eyes burning with a murderous, unhinged light. "The doctor. She orchestrated the whole thing. Find that black SUV. Bring her to me alive. I'm going to tear her apart."