Penny answered Leonard's unpatterned knock, saying, "Leonard, I'm not really up for company…" She stopped, frowned at Sheldon and asked bluntly, "Why is he here?"

"Sheldon has something he needs to say to you. Just hear him out," he pleaded.

She pursed her lips, clearly unhappy, but let the two of them inside. Leonard elbowed Sheldon in the ribs as he fidgeted, standing in the middle of her living area.

"I owe you an apology," he said stiffly. "I take full responsibility for the dissolution of our marriage." Penny gaped at him, speechless with shock. "There's something else you should know." He handed the documents to her.

Her face softened as she looked at the top paper. "Our marriage certificate - you kept it." Then she turned to the next page, and her features hardened. "And the divorce papers… why are you showing these to me?"

"I need you to understand why I have them. They're still in my possession because I could never bring myself to file them. The divorce was never processed. We're still married."

All the color drained from Penny's face. There was a flash of motion and a resounding clap. Sheldon cradled the side of his face that she had just slapped, too stunned to react. "You heartless bastard," she hissed. Then her face crumpled, and with a sob, she ran out of her apartment.

For several long moments, neither man spoke.

"Something you forgot to mention?" Leonard asked, shaking his head with a mixture of pity and disbelief.

"I don't understand. She said she wanted to get back together." Sheldon cast a wide-eyed, helpless look at his best friend, then winced and gently massaged his stinging cheek.

"Look at this from her perspective," Leonard said. "She got married way too young, so young she was afraid of what her family and friends would say. Then her husband-" He squinted at Sheldon, still half expecting this to turn out to be a bazinga. "Her husband proves her right by ditching her without cause or provocation - as far as she knows," he said, raising a hand to forestall Sheldon's inevitable protest. "She moves in with someone she thinks is a friend, only to have him turn on her too. All this time, her friends are urging her to move on, but probably none of them know the whole story. Despite how horribly you treated her, somehow she hasn't been able to get over you. When she came back, you accuse her of cheating, when the truth is that she's been waiting for you for years. Now you finally tell her that you couldn't go through with the divorce. You think you're being magnanimous, but in her eyes, you set her up. You let her think your marriage was over when it actually wasn't, so that when she found someone new, you'd make her a cheater. It's only because you really are the luckiest bastard alive and she's still hung up on you that she didn't sleep with someone else in the past few years. It's like you framed her. I'm surprised she didn't punch you."

All the color had drained from Sheldon's face. "I never thought of it that way," he said faintly. He turned frantically to his best friend. "What do I do?"

Leonard looked around the room for a moment, taking in the colorful decorations and soft furnishings which were so different from their drab apartment. This was what he wanted - a woman to come into his life and imbue it with warmth and happiness. But that woman would never be Penny. He wasn't sure how long it would take to get over his futile crush, but Sheldon was his best friend. He deserved happiness too.

They'd both heard Penny's footsteps as she ran up the stairs, most likely headed toward the roof for some privacy. He jerked his head upward. "If you really want her back, then it's your turn to make some sacrifices for her."

Sheldon paled but nodded.

"I guess you know best what would make her happy," Leonard continued with a rueful grimace. "But right now, you need to go apologize to her. Get down on your knees if you have to. Tell her you're sorry and that you were an idiot, and tell her over and over again until she believes you. There isn't anything I wouldn't do for a woman like her if she loved me. I mean it. Do you think even a Nobel Prize can compare to a love like that? You said you don't think you deserve her. If I were you, I'd spend every day of the rest of my life trying to measure up. You failed her once, but you've been given a second chance. Go be the man she deserves."

Leonard made it sound so simple. Yet Sheldon knew if he was to make his marriage work, he would have to struggle every day against his selfish and immature impulses. The analogy of the Nobel Prize applied here as well, he realized with a surge of hope. He would never win that ultimate acknowledgement of his genius without years, perhaps a lifetime, of hard work. Pursuit of that goal required dedication, persistence and sacrifice. The difference was that he could spend decades working towards a Nobel with no guarantees that he would ever succeed. Penny had been the one to come after him. He'd walked away once from the greatest happiness he'd ever known. Now it was his turn to pursue her, to convince her that he could put her needs above his own.

With a grateful nod to Leonard, Sheldon climbed the stairs. He found Penny looking out over the city with her arms wrapped tightly around her body. The metal door's rusted hinges squealed as he pushed it open. She didn't even glance his way, but he saw her swipe moisture away from her cheeks.

He took a deep breath, trying to find the right words. In the end, he just decided to borrow Leonard's. "I'm sorry. I was an idiot."

She still didn't turn to look at him, but her shoulders stiffened. He hoped it was a good sign.

He moved so he could just see the edge of her cheek, noting it was wet with tears. Then he sank to one knee on the dirty rooftop. That got her attention. She turned to look at him, her eyes wide with shock.

"For more than three years, we've both been miserable, and I'm entirely to blame. I thought you would be happy to hear we were still married, but I didn't understand how you might see it. When I walked away from our marriage, I wasn't trying to hurt you, but to protect myself from the pain I was feeling. I don't know how to make this situation right, but I'll do anything you ask of me."

She gazed at his face for a long time, and her expression was indecipherable to him. At last, she asked softly, "Was I ever the most important person in the world to you - more important than yourself?"

"Yes," he said with all the force he could put into that single word. "You threw my whole life into chaos… but I never knew happiness until I met you."

Fresh tears flowed down her face. "If you really want me back, I want you to promise me two things."

He quickly said, "I promise."

"You don't even know what I'm going to say," she objected.

He reached for her hand. "You are worth any sacrifice."

She shook her head, more in disbelief than denial. "This is what I want. I want you to promise me you'll never walk away from me again. And I want you to promise that no matter what problem comes up, we'll talk about it and find a solution."

He gaped at her. "Those are your conditions? You aren't going to ask me to move to Nebraska or give up sci-fi?"

"Why would I do that? I don't want you to change who you are. I love you. I never stopped loving you."

"I didn't love you the way you deserved, but I never stopped loving you either."

She smiled at him, and for a moment neither of them did anything more than gaze longingly in each other's eyes. Then Penny tugged on his hand, pulling him to his feet. "It's been three damn years. Don't make me wait any longer."

It was all the permission he needed, and he cradled her face as he tried to express all the love and gratitude in his heart. She rose up on her toes to meet him as he brought his mouth down on hers. She clutched at him, and he could hear a little whimper as she wrapped her arms around his neck.

A long time passed before the two of them came back inside, hand in hand. Their cheeks were flushed and their clothing slightly askew. In the stairwell between the fourth and fifth floors, she tried to smooth out his hair. "I guess we look like we've been fooling around," she teased.

"Not nearly as much as I'd like," he answered with a smirk.

She laughed but said, "After all he's done for us, Leonard deserves better than to spend the rest of Christmas alone. Besides, there's not much more we can do without condoms, and the stores won't open until tomorrow."

"I believe Leonard has some in his nightstand," Sheldon offered with a devious grin.

Penny laughed again. "I like the way you think."

Leonard looked rather surprised to see Sheldon and Penny come in. "So, you two look... happy, right?"

Penny beamed at her husband. "Yup, and a big part of it is thanks to you," she said to Leonard, giving him a hug.

When she stepped back, Sheldon looked back and forth between Penny and Leonard. Then he rather awkwardly put his arms around his roommate. "Thank you," he said solemnly, while Leonard's eyes almost bugged out of his head with shock. Glancing over at Penny, Sheldon gazed at her with such adoration that Leonard shifted uncomfortably.

"Uh… if you guys have somewhere you need to be…" he began.

Penny took Sheldon's hand again as she explained, "Actually, we've already decided that there's nowhere else we'd rather be than here with you. You saved our marriage, after all. There's plenty of time for us to be alone later."

"I'm going to go pack a bag. I'll be staying over at Penny's tonight," Sheldon announced and headed toward the bedrooms.

Leonard drew in a long breath and then let it out slowly. "I guess I'll be losing a roommate."

"This is a two-bedroom apartment," she teased, but then grinned to show she was kidding. "But I think it's best that we have our own space. We'll work something out, but one thing's for sure: you're Sheldon's best friend, and nothing's going to change that."

A few minutes later, Sheldon emerged from the back hallway with a black duffle bag in hand. His eyes sought out Penny's. When she lifted her eyebrows at him, he nodded and then held up four fingers. She looked slightly disappointed, pursing her lips while she flashed a brief, exasperated glance at Leonard. Then she shrugged.

Leonard looked back and forth between the two of them curiously. "Wow, you guys really have that couple's nonverbal communication down cold."

"We had to. Have you seen him at those departmental mixers?" Penny said with a giggle.

Sheldon frowned in mock annoyance, but then joined his wife on the couch. They sat side by side, but this time, Penny was sitting partially on Sheldon's beloved 0,0,0,0 spot so she could cuddle close to him. He reached for her hand and twined his fingers with hers. "What are we watching?" he asked as Leonard put a DVD into the player.

"Penny let me pick: It's a Wonderful Life. It's my favorite Christmas movie," Leonard answered as he joined them on the couch.

"I'd prefer to watch a Doctor Who Christmas special," Sheldon grumbled.

"We can watch it together tomorrow. It's a Wonderful Life is a classic about second chances and learning what's really important in life. I think it's perfect," Penny said.

Sheldon lifted their intertwined hands to brush a kiss across his wife's hand. "Perfect," he echoed, as he gazed into her eyes. It was more than perfect; it was a Christmas miracle.