A billionaire had already spent more than $3 million trying to save his mysteriously weakening twin sons when his private doctor laughed at me for thinking a nanny might notice what specialists had missed. Hours later, I found something hidden in plain sight outside the boys’ bedrooms, and the terrified look on a housekeeper’s face told me their illness might not have been a mystery at all.

In the pitch black, Graves fired the taser. The twin probes slammed into the steel casing of the furnace six inches to my left, discharging with a brilliant blue arc of electricity that illuminated the room for a fraction of a second.

I didn't wait for him to reload. I threw my entire body forward, tackling him low at the knees.

We crashed to the concrete floor together. Graves was heavier, stronger, and trained for close-quarters combat, but he was disoriented by the dark and terrified of inhaling the aerosolized cloud pooling around our heads. He threw a heavy, blunt elbow that grazed my cheekbone, sending stars exploding across my vision, but I held on, clawing at his tactical vest until my fingers found the handle of the combat knife sheathed at his chest.

I ripped the knife free and drove the heavy pommel directly into the side of his jaw.

Graves grunted, his grip slacking as his head snapped against the concrete. Before he could recover, I rolled off him, scrambled to my feet in the dark, and lunged through the doorway, slamming the heavy steel fire door shut behind me and throwing the external manual deadbolt.

Graves threw himself against the steel from the inside, cursing violently, his fists pounding against the reinforced panel. But the seal held.

I leaned against the cold stone corridor wall, gasping for breath, coughing as the residual fumes burned my trachea. I checked the knife—a six-inch serrated tactical blade—and tucked it into the waistband of my leggings.

I had destroyed the delivery system, but Blake still had the twins.

I sprinted back up the concrete stairs, bursting through the service pantry into the main ground-floor corridor.

The front entrance was wide open. The cold, wet Atlantic wind was whipping through the foyer, scattering papers across the marble floor.

Outside, on the circular drive, Blake was already loading a stretcher into the back of the black Mercedes ambulance. On the stretcher lay Leo, completely limp, an oxygen mask strapped over his tiny, pale face. Lucas was already inside the vehicle, strapped into an adjacent gurney, crying out weakly for his father.

Beside the driver's door stood two private security contractors wearing black tactical jackets, their hands resting near their holstered sidearms.

"Blake!"

My voice cut through the wind and the idling roar of the diesel engine.

Blake paused on the ambulance bumper, his hand on the door handle, turning his head slowly toward me. When he saw me—covered in soot, blood dripping down my arm, hair wild and eyes blazing—his expression transformed from smug condescension to pure, unadulterated fury.