"Sammy!"

The feral roar turned each of the shaven heads towering over the youngest Winchester.

"Dean!"

Sam's voice cracked; somehow the thirteen-year-old was more distressed by his adolescent squeak than by the wrench-wielding young inmates surrounding him. His lack of fear could have been due to his immaturity; but more likely it was a result of the unshakable confidence he had in his older brother.

Said sibling collided with the pack of juvenile delinquents with the force of an angry Wendigo, knocking two to the ground with the first swing of the fire-extinguisher.

Sam scrambled up, half-tripped, and scooted to safety behind Dean, who hefted the improvised weapon for another blow.

The youngest Winchester could feel the rage and frustration radiating from his brother's body; when two bullets had put Dad in the hospital, and close proximity to a mysterious murder had put the boys in Juvenile Detention, it had been all Dean could do to keep his younger brother safe.

The inmates had singled Sam out instantly.

He was gangly, awkward, and naive. Granted, the thirteen-year-old was a better shot with a sawed-off than most people, but the first day in detention he'd tried to make friends by giving away his lunch. It was quite obvious the kid was toast.

From the moment the iron gates had swung shut behind them, Dean had been on constant alert. No-one moved towards his brother without his knowledge. He was armed at all times, ready to strike at a moment's notice.

It was now day three; Dean had slept for a total of five hours. Eyes bloodshot, he prowled rather than walked, and his scowl could have been growing canines for all Sam knew. He'd seen his brother like this once or twice before - only when Dad was gone, and Sam was in imminent danger. He called it Dean's "predator mode."

The fire-extinguisher struck again; the echo sharp as it connected with skull.

"Dean;" Sam gained his feet, pulling on his brother's jumpsuit as he did. "It's okay. Let them go."

Part of "predator mode" was hearing loss. Sam tugged harder, strength returning to his voice as he saw the blood pouring from the mouth of Dean's victim.

"Dean. Stop. That's enough!"

The other three delinquents had long-since deserted their comrade who was now curled into a ball on the concrete pad, his cries for mercy unheeded.

Another hollow crack as metal connected with bone.

"Dean!"

Something twisted uncomfortably inside Sam, and his mouth went dry. Stop Dean.

A sudden surge of adrenaline seized him and he grabbed his brother's arm, fingers digging into the straining muscle.

"Dean!"

At the touch his brother whirled - snarl canine, eyes blood red, extinguisher raised.

Sam cringed backward, the metal canister nearly colliding with his raised arms.

A second of silence followed.

Aluminum pinged as the extinguisher clattered to the pavement. Dean dropped to his knees, the feral creature giving way to a shaking seventeen-year-old.

"Sammy, I'm so sorry."

Sammy.

"Sammy!"

It was that same, guttural, animal yell. I'm coming for you.

Predator Mode.

As Sam clenched his knife, his breath seeming to desert him as he heard his brother advancing through the halls of the bunker.

It was ironic; it was only the desire to protect that could turn Dean into a monster - a monster that would turn on the very thing it cared for most.

Sam gripped the knife tighter in anticipation, while at the same time realizing that he would let it slip through his fingers before fighting his brother.

Stop Dean.