Disclaimer – I don't own Castle or any of the characters. Although I will admit wishing I DID own Castle after the picture of NF that was on the website from Comic-Con. He really IS ruggedly handsome!

Kate Beckett winced as her hand slammed into a banister as she took the stairs two at a time, yelling his name. "CASTLE!" Her pace nowhere near matched his. She had never seen Richard Castle move this fast. She thought back quickly to the events that had set this chase in motion. He had visibly paled, but revealed nothing to her, when she'd told him the destination address. His eyes had darted nervously between her and the tony Manhattan building when they'd arrived, but it was one short sentence from Esposito that had sent him barreling up the heavy oak stairs. "The vic's daughter found him."

She could hear his voice above her, wild and strangled with both adrenaline and fear. He was saying a name, but she couldn't make it out…Kara? Tara? "CASTLE!" she called again as she finally reached the landing. The floor beneath her feet was an ornate, elaborate pattern of marble and granite. A round glass and mahogany table was before her, topped with a large bouquet of fresh flowers. She caught just a flicker of his tan overcoat disappear into a room just off the main foyer. She rounded the corner and the scene before her left her speechless.

Arms clothed in a thinly knit ivory sweater circled his neck. His arms around a woman, one at her back, the other pressing her honey blonde braid into his chest. He pressed soft, gentle kisses onto the top of her head, his eyes closed against the gut-wrenching sobs overtaking her slender form. Kate had never felt more uncomfortable – watching as her partner, her Castle, consoled this unknown woman.

She turned away, closing her eyes to the quiet reassurances he was offering, "Shh…I'm here. I'm right here, it's okay…"

She glanced at Ryan, who only shrugged, offering no explanation as to this woman's name or position in Richard Castle's life. Esposito leaned into toward his boss' ear. "Zara Chase…she's the victim's daughter – Conrad Chase. 68 years old, major real estate developer. Single GSW to the head. I have no idea what her connection to Castle is."

Kate felt the color drain from her face. Zara….Z…. She shook her head against the thoughts forming in her head. His watch…the one he'd started wearing after his last birthday. He had taken it off one day after an unfortunate run-in with an irritant that left a nasty rash on his arm. She'd picked it up to tease him about the Tag Hauer "knockoff" being the cause of the rash when she noticed the inscription on the back. "Happy Birthday! Love, Z"

The three turned back to the couple to find that Rick had tucked the petite blonde into his side, one arm still around her waist while the other held his cell phone to his ear. She wiped tears from her eyes with the back of her hand and stared down at the lifeless body of her father on the blood stained mahogany wood. "I don't know, Mother," Kate heard Castle say "all I know right now is that Conrad is dead and Zara found him."

He must have been content with Martha's answer because he stabbed the disconnect button with his thumb and jammed the phone back into his pocket. "Let's get you out of here," he said gently to Zara, his body never severing contact with hers, breezing past Beckett to lead her back into the foyer.

"Castle," she said his name again, this time through clenched teeth. Who the hell was he to remove her only witness? She stalked after him with Ryan and Esposito hot on her heels. She swung the door to the kitchen open and stepped inside to find Castle pulling out a chair and ordering Zara Chase to sit. "Castle, what the HELL?" she demanded.

Jolted from his thoughts, Rick looked at her with wide eyes. "Beckett?" he said, his tone surprised, as though he'd forgotten he'd arrived on the scene with her. "Yeah, Castle. Remember me? "

His eyes darted between Kate and Zara. "Of course I remember you," he answered nervously, "what a ridiculous thing to say."

Kate laughed. "RIDICULOUS is you making out with my witness over her father's dead body." She ignored Zara's reactive sob to the word "dead".

"Making out?" Castle thundered; his hands immediately at his hips. "Making OUT? If you think THAT was making out, then I have really got to…" He let the thought trail off, turning back to glance at Zara.

Kate scanned the blonde's slender form, taking note of the wisps of hair stuck to her cheeks by her tears, the redness of her throat; her hands shaking as she wiped the blood from them on a cloth Rick must have handed her. On the third finger of her left hand was a ring. Kate couldn't tell from her current vantage point what the material was – too white to be gold, too luminous to be platinum. It formed a delicate knot over the top of her slender finger as Zara half-heartedly cleaned it.

"Miss Chase," Kate said quietly.

"Zara," the blonde answered, her voice devoid of emotion. "My name is Zara."

"Zara," Kate repeated with an annoyed tone that made Rick unconsciously roll his eyes. "My detectives say you found your father?"

She sniffed and closed her eyes tight as another sob threatened to erupt. "Yes, he, uh, wanted to meet with me. I punched the button for the elevator from the lobby and I heard what sounded like a…" Zara began to hyperventilate and Rick was behind her in flash, his arms wrapped protectively around her shoulders.

"A gunshot," she continued, seemingly reassured by Rick's touch. "I dropped my bags and took the stairs. I got to the door of the study and he was lying there…there was so much blood. I felt for a pulse…and…and…there was no pulse." Her anguished tone had Rick burying his face in her hair. "I called 911, and then started CPR, and…"

Zara was cut off by another familiar voice in the hallway, yelling at the uniformed officer to "get the hell out of my way." Ryan pushed the door open and was nearly overrun by Castle's mother, Martha.

The blonde lept from the chair and into Martha's arms. "My baby," Martha cried, "my sweet baby girl, I am so sorry…"

Kate's confusion was suddenly compounded. Baby girl? Richard Castle was an only child.

"Oh God, Mom…" Zara said quietly, clinging desperately to the older woman.

Kate looked to Castle for clarification. He swallowed hard and looked at her with tears in his eyes. "Zara is, uh, my little sister."