Authors Note: This is an established pairing fic, set in an Alternate Universe where they've been married for years, Mary never died, and where Mycroft also has a wife and child. Based on events in The Convergence Roleplay Forum and headcanons with Best Damn Avocado (Angie). Mycroft's wife is based on Supernatural's Naomi.

While the setup to the events in this story could have been include in many other chapters, it wasn't the focus I wanted. There are several other Natlock stories to check out if you wish to read a 'falling in love' story.

Natasha Romanov-Holmes tore through the old battleship, running faster than she ever had. Like a bullet loosed from a gun. Nothing had been more important than what lay trapped behind two inches of steel battleship door.

By the time she reached the door, the pounding of her heart was the only sound in her ears. Everything else had been muted like she was underwater. She slammed a miniature explosive charge on the door and it snapped open with a deep thud and an expansion of white fog.

The fog spoke of death. The gas that had filled it made her cough hacking breaths as she stepped inside, even as it dissipated in the negative pressure.

The light from the single bulb in the ceiling cast a ghostly haze over the too still body in the nearest corner. His mess of curls had matted with cold sweat, his face was turned downwards, his back did not rise or fall in breath. Her mind couldn't fathom why that would be. What could stop Sherlock Holmes? His strong arms had wrapped something up in his heavy coat as if trying to block out the poison gas.

Not something. Someone.

Natasha collapsed just within reach, what little strength she had left dissipated like the gas that had taken them away.

- Too Many Minutes Earlier -

In a maniacal effort, Sherlock Holmes struggled with the locked door. His curly hair flopping over his forehead and his Belstaff swaying around him indicated the force of his attempts. But for all his strength and brains, he could do nothing against the steel trap.

"NATASHA!" He pounded his fist against the airtight container's only exit. The gas leaked in slowly through a vent that would have been just big enough for Basil their cat to squeeze through. Not a fully grown man.

"Daddy?"

Nor a five-year-old boy.

Sherlock should have accepted the facts as they were. There was no way out of this. He'd failed already. He'd failed hours ago when he'd not prevented Sterling's kidnapping. He'd failed when he sent Natasha one way and he'd gone the other. He'd failed when Sterling had been crying, and he'd failed when the Russian hitmen trapped both of them in this box of death.

None of this was about him, it was all about Natasha, and taking everything she loved away. They wanted to leave her alive, but alone. Kidnap the child, get to the husband, kill them both. Sherlock just hadn't been good enough to stop them.

He wished he had time to apologize to her. To hold her one more time.

There was a proper time to die, for everyone, for him. Today was his time. Not Sterling's. The small respirator mask in his coat would take care of that. The just in case measure would save the life he and his soulmate had made together against all odds.

He crouched so he could be eye-to-eye with his clever little boy, taking Sterling's head in his hands. The boy's green eyes had again filled with tears, and his whole body was shaking. He had to know exactly what was happening, he was too clever to miss it.

Sherlock's words were gentle. "Sterling, look at me."

"Daddy, I'm scared."

"I know," Sherlock breathed. He closed his eyes and pressed his forehead to Sterling's. "I'm scared too. But we're going to be very brave now. I need you to listen to every word I say and do everything I tell you to do. Can you do that? Promise me."

Sterling's fingers flexed into Sherlock's coat. "I promise."

"Stay still."

Sherlock got the respirator out in a flurry of motion, fixing it firmly over Sterling's mouth and nose. It'd been something he'd snagged from Natasha's old S.H.I.E.L.D. supplies, meant for an adult, but could be modified and it had its own tiny supply of oxygen. Enough to keep Sterling alive for a short time. But it was not enough for the both of them. Not that there was any way Sherlock would risk taking it off of the child after the gas had come in.

"Close your eyes, Sterling, keep them closed whatever happens," Sherlock said gently.

Sterling stood very still, tears trailing down his cheeks. He nodded when Sherlock asked if he could breathe and reminded him to take slow breaths.

Sherlock stood up, glancing at the vent which still poured the fog of toxic gas out into the empty space. Inert gas to displace the oxygen in the room, with a toxic property to ensure they died. Also something new. He calculated the room would be full in four to eight minutes. Four to eight minutes to live, to hold his son, to prepare himself. He moved them to the corner furthest away from the vent and closest to the door. In the smallest hope, Natasha would find them in time. It was there he settled on the cold ground. "Come here," he said, gently tugging Sterling's hand and helping him settle on his lap. Just like they'd done a thousand times before. Except instead of reading a book or peeking at the microscope, they were preparing for Death's visit.

The boy was getting big. During the last trip to the doctor, they'd estimated he'd be as tall or taller than his father someday. Sherlock felt an intense sadness he'd not live to see the puzzle of this intriguing life grow. Too late for regret now, not when so much was at risk.

Sherlock wrapped Sterling up in his Belstaff, blocking out as much of the gas as he could that way too. And like a lid on a tea pot, Sherlock tucked his head overtop of Sterling and buried his nose in Sterling's curly dark hair, still faintly smelling of the hotel shampoo. He surrounded his son in a shield of his own body and his most precious garment. It might as well have been armor. He felt the quivering body he'd cared for and tickled and held. Fear so intense. Sterling was not going to be the same after tonight, Sherlock knew that much. He only hoped there'd be an understanding in time, he was doing what he had to.

Sherlock took a deep breath. "Sterling?"

"I'm here." The words came muffled from inside Sherlock's coat and behind the respirator.

Sherlock closed his eyes. He didn't want to see the darkness of his execution room. "William Sterling, I don't know what's going to happen next," he started quietly. "But your mother is going to come and find us, she's going to pull you out of this and bring you somewhere safe. I want you to try to sleep in the meantime. But when she finds you, I need you to tell her a few things for me, okay?"

"Why can't you tell her?"

Sherlock's already broken heart snapped completely in two. Tears burned his eyes, and he was confident it wasn't the leaking gas. "Because I…because I don't know if I'm going to make it out of this," he confessed. "But you are. With that mask, you can breathe. I am your father and I would do anything to keep you safe. That's what dads do. I don't want you to ever forget that. I love you so much."

Sterling's crying was audible and he shook like a leaf in Sherlock's arms.

"Shhh…." Sherlock knew the tears were out of pain and fear. He didn't try to stop them, just comfort through them. "I need you to tell Mummy that I love her too, okay? And that I'm sorry. None of this was her fault. Tell everyone we love that I loved you. Please, will you do this for me?"

"I…I pr-promise."

"Thank you." Sherlock coughed hoarsely, recalculating the time in his head. There was just never enough of it in the end. He needed more time. For his family: for Natasha and Sterling and John and Mary and Rosie and Mycroft. For his friends: for Molly and Greg and Mrs Hudson. If only he could just hold on a little longer.

But his great mind knew better.

His body shook with the effort but he didn't move from where he was his son's shield. "Sterling…I promise…I love you…don't forget that. Don't ever…forget. You're…going to be…amazing…You're mine, always will be…sleep now…I've got you…"

Sherlock's stream of words continued through the coughing until he just couldn't hang onto consciousness anymore. The gas filled his lungs, stealing his oxygen, slowing his brain, stopping his heart. Death by asphyxiation wasn't so bad. If he wasn't so damn afraid. Oh God please let me live.

And there, still wrapped around like a vise to protect his greatest legacy and long minutes before help arrived, William Sherlock Scott Holmes' body stilled.

He would be found just too late by the woman who'd entered his mind and then heart many years before.