A/N: I came up with a 'what if scenario' crossover between Fallout: New Vegas and Fallout 4. My story follows the general plot of New Vegas but I have definitely taken large creative liberties so many aspects won't be canon. It takes place shortly after the events of New Vegas but before the beginning of Fallout 4, so spoiler alert for both games. DLC content is not included in the story. There will also be a Boone x Courier romance. The Courier's name will be Mary since I googled 'generic female name' and that was the first one that came up. Like my previous story, I will keep her description fairly vague so you can insert your own version of the Courier in her place. I hope you enjoy!

Prologue: Curiosity

MONTHS AGO…

Don't do it.

Mary knew the routine by now. Jane, Mr. House's securitron companion, would access the wall terminal in the penthouse of Lucky 38 at exactly 8:25pm. The Courier pretended to preoccupy herself on her Pip Boy.

8:24pm.

The Courier was no doctor, but she knew she had an illness. Because she couldn't let this go. She had to see him. She had to know.

She turned slightly, so that Jane's metallic body twinkled in her periphery. Seconds later, the robot was on the move.

She hesitated for a brief moment.

Then she followed.

With her mechanical efficiency, Jane accessed the terminal keypad. After an affirming beep, a hidden door opened, and Jane rolled inward. The Courier waited a few seconds, then slithered through the hidden entrance a half a second before the door slid shut. She prayed her hack was successful, otherwise her trip was going to be impressively short.

The hack had worked. The securitrons guarding the inner chamber let her pass without so much as a twitch. Good thing, too, considering she'd helped Mr. House upgrade them.

Jane was surprisingly oblivious to the human presence behind her. Instead of turning to face Mary, she barreled across a metallic platform to a closed, glowing chamber. The Courier cringed as her boots clanged against the metallic floor, but Jane was preoccupied with the distant chamber. The Courier crept slowly forward, cursing at every clatter and echo she made. Finally, she ducked under a terminal and waited. She knew she had exactly ten minutes before Jane would leave and return to her usual position near the penthouse elevator doors. Robotic programming was delightfully predictable.

Despite the hissing of joints and burning of muscles, the Courier remained hunched under the terminal. And waited.

Jane was speaking now, though the words were muffled by the hum of electronics. The tone was clear, though. Sweet, soothing, comforting. The way a mother might coo a child.

A rhythmic hum vibrated against the railing minutes later as Jane rolled away.

After a few additional seconds, Mary raised herself and stepped towards the shrill white light of the distant chamber.

To some extent, she knew what she was going to see weeks before this moment. The instant she saw large, black cables leading from Mr. House's monstrous monitor into a poorly hidden secret room, her suspicions were aroused. After all, Mr. House was no computer program, no securitron. He'd once been a living breathing man.

And, centuries later, he still was.

He resembled ghoul more than man now, a decayed skeleton with desiccated skin still clinging to brittle bone. His hands were gnarled with long, claw-like nails. Wires had been plunged into various areas of his body. Time had caused his flabby skin to grow over and around the wires in fleshy webbing. His head, now large and bobbly compared to his stringy body, was ensconced in a heavy flashing helmet. His eyes were open, foggy and colorless.

This. This…thing was what she'd been working for this entire time.

Without thinking, the Courier placed her gloved hand atop the glass chamber case in an inexplicable gesture of sympathy. All this just to save New Vegas. The sacrifice was too great.

WHACK!

Mr. House's shriveled hand slapped against the inner glass of his self-made prison. His glossy eyes rolled in her direction and his head lolled to her side of the chamber.

The Courier gasped, stumbling back. Instinct kicked in, and she turned to run. She could hear the grated, muffled voice of the withered man yelling, but she sprinted away before she could discern the words.

To her surprise, the securitrons did not attack her as she made it to the elevator. In fact, the only noise she heard was an annoyed "Well, I never!" from Jane as she pushed past her. She gagged for air, her guts cramping. The elevator doors couldn't close fast enough.

Mr. House would never forgive her for this intrusion. Their alliance was over.

She thought she never would, never could come back to the Lucky 38.

And yet, one day, she would.