Unwrapping his scarf and juggling his messenger bag, keys, and the handful of mail, Sheldon unlocked the apartment door and tossed his keys into the bowl, taking a happy, deep inhale of the air in the still apartment. He had an admittedly dim recollection that Howard was spending some vague holiday observance with Bernadette, Raj was giving a lecture while coasting on his latest coincidental discovery of some otherwise unexceptional astral body, and Leonard actually wanted to attend the physics department holiday party. Sheldon had the television, couch, kitchen, room to himself, at least for the moment. The feeling was altogether giddy, and as he dreamily slid his imitation Star Trek mirror universe dagger letter opener into the open folds of the pastel-colored envelopes and slid out the various glittery, ribbon-bedecked cards, he imagined a few uninterrupted hours of perusal of the latest European physics journals. It was only fair that he share with Leonard the latest developments in his own research path, since Sheldon's own was so particularly groundbreaking.

With three cards and a power bill on his desk, Sheldon frowned at the configuration of cards currently standing on the mantel, and arranged them to his satisfaction, happily without the snide remarks or dismissive snorts from Leonard, Howard, or Raj. He traced his footsteps back to the middle of the room and scrutinized his work, moved the second card from the right an inch to the left, and gave a nod of approval.

When he was dialing the number for the Chinese restaurant, Sheldon paused. Penny. Yes, Penny was at the Cheesecake Factory company party while Leonard was at the physics party. They had debated, each graciously agreeing to go to the other, until Sheldon, equally graciously, had pointed out that the two had absolutely nothing to do with each other, each significant other would be bored at the other's party, and the best solution would be to go separately. To which he received a glare from Leonard for his trouble, and a wrinkled nose from Penny, but fifteen minutes later they'd appeared to independently come up with the same solution. So Penny would doubtless stumble in to her apartment at three o'clock in the morning, while Leonard paced, still buzzing a little from the ridiculous fake synthehol punch, and Sheldon would have to put on a Feynman lecture to drown them out.

After briefly debating writing down the sequence of events, sealing it in an envelope, and performing some skit which involved an improvised turban and the assumption of an Amazing Kreskin persona, Sheldon dialed the last digit in the number of the Chinese place and placed his order.

Four hours later, empty cartons all stacked in the trash, a tall sweating glass of Mountain Dew at his elbow, and the cursor of a text-based RPG flashing on his screen, Sheldon was unpleasantly startled when someone stamped hurriedly up the flight of stairs just outside his apartment, then pounded furiously on the door before scratching a key in the lock. Imagining the last time Leonard had raced up the stairs during a lactose-driven incident, Sheldon pushed back his desk chair, but had no time to stand before Penny was standing in the doorway, keys still dangling from her hand. In flagrant contrast with her standard Cheesecake Factory uniform, Penny was wearing a tight red tank top and black leather miniskirt with tall-heeled black boots that definitely emphasized her bust and derriere and limited her speed in any sort of ambulatory competition, Sheldon automatically noted. Then, brow furrowed, lips pursed, Sheldon raised his gaze to Penny's face, to see her cheeks stained with trails of mascara, her usually carefully arranged hair in artless tangles, and her eyes wet and red.

"Sheldon?" she half-gasped out, her voice rising on the last syllable of his name, and slammed the door behind her.

"Of course," Sheldon answered irritably. Penny's attire left her arms and the majority of her legs bare, but while arranging her closet during his well-intentioned organization effort soon after her arrival, he had mentally catalogued several appropriate examples of outerwear, and was just preparing to ask why she had not left her apartment in the zippered leather jacket when Penny reached for the afghan draped across the back of the couch, revealing a line of livid oval marks in the underside of her upper arm.

"If you're waiting for Leonard, I haven't yet heard from him— if you would rather wait in your own apartment."

Penny shot him a glance that made all her other caustic glances almost affectionate in comparison. "Shut up, Sheldon." She crossed her legs, wincing a little, staring fixedly at the television, which was displaying a subtitled anime episode.

Sheldon glanced at Penny's legs. A red welt was just visible under the hem of her skirt.

"If you found yourself in an amorous encounter at the party—"

It was part of what Leonard called their 'banter,' and generally would have provoked a stuck-out tongue or some sort of disparagement of his admittedly underdeveloped social skills, but Penny, instead of doing anything he would have expected, wound up her arm and, screaming "Shut. Up. Sheldon!", flung her cell phone at him. Years of Missy's juvenile torture had given Sheldon the muscle memory he needed to duck away from the projectile, and it struck the edge of his laptop monitor, crashing noisily against the opposite wall. Sheldon, in an indignant flutter, inspected his computer thoroughly until he was convinced of its relatively unchanged status, then turned back to Penny, face flushed, in a towering anger.

Leonard suddenly opened the apartment door, interrupting Sheldon mid-indignant inhalation, and immediately ran over to Penny. "Oh my God, are you okay? I came as fast as I could—"

"Leonard," Penny said, and then they were wrapped up in each other's arms and Penny was sobbing incoherently, and Sheldon turned back to his computer, running it through a more thorough diagnostic. When Leonard asked if he could leave the two of them alone, Sheldon disconnected his laptop without a word and stalked conspicuously to his bedroom. He cued up a Feynman lecture, but Penny let out another fluttering sob from the other room and Sheldon found himself unable to press the play button.

For once, Sheldon eavesdropped, his initial discomfort turning to horror.

--

Leonard, and more particularly Penny, didn't exactly come to Sheldon and explain the situation to him. Instead, after Penny was presumably quieted down in Leonard's bedroom, Leonard came and said that Penny would be staying with them for a few days, maybe a little longer, and there was no pleading or uncertainty in his voice. Sheldon, after subjecting him to a detailed litany of all the various ways Penny's carelessly thrown cell phone could have destroyed a piece of delicate computer equipment, just nodded, and Leonard walked back out without a word.

A week later, Leonard, Raj, and Howard disassembled Penny's bed and moved it into Leonard's room, Howard cracking jokes all the while, and Penny wore sweatpants or jeans, long-sleeved thermal shirts, and actually cracked weak smiles at Howard's lame jokes.

In his sporadic investigation of general social paradigms, Sheldon had figured out this one out soon after Penny had moved into their building. Penny, as a female, needed to treat Leonard, her current partner, as an alpha male. As Leonard was her designated alpha male, certain tasks fell to him, like the recovery of the television set from an ex-boyfriend that had ended so abysmally for him and Sheldon. When she was physically threatened, as laughable as the concept might seem, Leonard was the person she needed to turn to for protection. While Sheldon was under no illusion that Leonard was less than intimidating physiologically, the paradigm still stood.

So Penny was surrounding herself with four less than imposing examples of masculinity. The response was predictable, in psychological terms, according to the articles he read at work. Though he generally dismissed such 'science' as below contempt, he did see some small use in it, and looked thoughtfully from his computer screen to Penny's cell phone, which Howard had managed to repair with no loss of data. Though Howard had given him a dirty look when Sheldon had pointed out how useful his master's in engineering had proved when he was performing tasks easily duplicated by subliterate teenagers in retail outlets throughout southern California.

"You don't always have to be so much of a dick, you know."

"How is drawing a perfectly logical and reasonable parallel between the two acts considered unacceptable behavior?"

"Because it was a favor," Howard hissed, his fist nervously compressing a steel spring. "They would have had to recondition her phone anyway, and when you do something to help someone, you don't have to show off when you do it. That's the point."

Sheldon raised a slender eyebrow and took Penny's phone back, considering it.

Now he opened a new browser window and deftly keyed in the address of another website, one Howard had begged him to find during the Great America's Top Model Search of 2008.

Sheldon didn't have to show off. But, to be honest, he never actually tried.

--

"I'm sorry I yelled at you," Penny said apologetically when Sheldon returned the phone to her, the case newly cleaned and buffed, the screen pristine.

"You were under a good deal of emotional distress," Sheldon said primly. "I am given to understand that is generally an acceptable excuse for otherwise destructive behavior."

Penny's head snapped up and she narrowed her eyes at him, questioningly, but he returned to his desk chair.

"Do you expect to stay in our apartment much longer?" Sheldon asked, keeping his attention on his computer screen. The question was practically perfunctory; Penny's haphazard laundry technique had spilled out of Leonard's room, into the hallway, their shared bathroom, and even to a little-used corner of the living room. While Leonard had strictly forbidden Sheldon to ask Penny about any sort of rent arrangement, for the past two weeks she had yet to return to the Cheesecake Factory, had not returned to Iowa for any sort of winter celebration, and, more often than not, the recycling bin was a few wine or liquor bottles heavier when Sheldon woke up in the morning.

"I hadn't really thought about it."

"I was wondering if the quality of your sleep, and mine, might be improved if you procured some prescription sleep aid."

When Sheldon glanced back at her, Penny was flushed. "I— I didn't know you could hear from your room. I'm sorry."

Sheldon, in a supremely magnanimous gesture on his part, shrugged. "I have calculated, and a permanent investment in disposable foam earplugs may prove slightly more expensive, in the long run, than a temporary dependence on a sleep remedy. Although the potential side effects themselves do rather detract from the appeal. Should you pursue that avenue, I will insist that Leonard install a padlock system to keep your nocturnal wanderings to a minimum."

Sheldon's eyes widened as Penny wrapped one arm around him from behind and dropped a kiss on his temple. "You big old softy," she murmured, snuggling a little deeper into the afghan that always carried the faint clean scent of her when she was away, because even if she did nothing much else these days, she did shower to what even Sheldon considered a slightly obsessive degree.

"I just wish to keep our foodstuffs safe from any inadvertent devouring."

"Sure," Penny said, sitting back down on the couch.

"Do you wish to proceed to disc four of Battlestar?"

"I watched it yesterday." Penny drew her brows together in a pantomime of apology when he turned around, accusatorially. "I had to find out what happened next. But if you want, we can watch it with director commentary?"

Sheldon sighed, somewhat mollified. "I will allow that, in lieu of the viewing comprehension quiz."

"Great," Penny sighed. "Wow, Sheldon, it's just like Christmas."

--

After a particularly unpleasant run-in with Kripke, Sheldon marched back to his office and locked the door, then activated the passive webcam feed from the apartment. Penny was curled up on the couch, her head still on the middle cushion but her hair spilling onto Sheldon's cushion, with Howard explaining something through the use of exaggerated hand gestures and an overly animated expression, most of which was entirely ignored by his audience. Penny, when she was alone, was subject to crying fits, but even Raj's silent presence in the apartment was enough to keep her from most emotional outbursts, and she had spent less than two hours alone since moving into their apartment.

Sheldon closed the window on the link, then crossed to his whiteboard, scowling. Kripke's most recent heckling had involved his impasse over the constant in Sheldon's equations, and, recommitting his progress to his eidetic memory, he swiftly erased the entire board and uncapped his freshest black marker.

No police report, he wrote.

Sleep disturbances.

Emotional disturbances.

He ended with the name Penny had gasped out that night, in her tearful recounting to Leonard, the phone number he had discovered in her cell phone, the address a desultory search of a classified database had revealed.

It was not the most elegant solution.

But someone had to be the alpha male.

--

"What's this about, Sheldon?"

Penny glanced around her apartment, somewhat bemused. In a fit of energy, Sheldon had cleaned it a week before, instituting organizational methods and a custom-designed labeling system in a frenzy that had left him feeling supremely accomplished. All the spoiled and rotten food from Penny's refrigerator had been disposed of, the Penny Blossoms and winter shoes sorted into their designated cubbyholes, and after a second shampooing of the carpets, Sheldon would almost feel at home.

"I may be mistaken in believing this to be a rather delicate topic, and since in these situations it always seems more prudent to err on the side of caution—"

Penny made a swift, impatient gesture. "Cut to the chase."

Sheldon stopped and just looked her over. Under the makeup, purple half-moons of exhaustion shone under her eyes. She was thinner, and she kept her back against something solid, facing the door, even though it was bolted and they were alone. He nodded swiftly to himself. He'd made the right choice. Not that he'd ever doubted it.

From behind his back he produced a Polaroid. The subject, in life a square-jawed, thick-browed muscular man, was slack, features twisted in pain, in death. As Penny stared at it, her eyes shimmering with fresh tears, Sheldon flipped it over and showed her the date and time stamp.

"The man who raped you, Penny," Sheldon said quietly, keeping his gaze on her face. "I killed him. For you."

"Sheldon?" Her voice was quivering, just the way it had been that night she burst into the apartment with mascara trailing down her cheeks.

"So you can sleep again. You don't have to be afraid of what's behind the corners in the dark. You can go back to work. You can..." His hands fluttered, and a bit of his old arrogance slipped back in. "Fritter away your time the way you used to."

Penny shook her head. "Sheldon— you— they'll find you—"

Sheldon drew himself up to his full height. "Penny, did you suffer a head injury today? Concuss yourself on the refrigerator door? I am Sheldon Lee Cooper, Ph.D. Despite what you've seen on mainstream police procedurals, a moderately intelligent criminal is fully capable of outwitting law enforcement personnel, and I, Penny, am far better than 'moderately intelligent.'"

Penny just stared at him for another moment, then back at the Polaroid, studying it minutely. Then she turned on her heel and darted into the kitchen, yanking open drawer after drawer. "Matches!" she cried, exasperated.

"Drawer under the microwave," Sheldon responded immediately.

Penny, her lips pressed tight shut, struck match after match, even as Sheldon protested that she had certainly wasted twice as many matches as the job required, a furious gleam in her eyes as she tossed the picture into the spotless sink and the last tongue of flame obliterated the image.

Sheldon crossed to the sink and conscientiously opened the tap, sending a stream of cold water over the still-smoking picture.

Penny turned. "You're crazy," she said, her gaze searching his.

"My mother had me tested," Sheldon replied, offended. "I weighed the benefits against the admittedly negligible risks, and this was the only logical response."

"Did he suffer?" Penny's voice was a savage whisper.

"The poison I employed is considered inhumane for use on white lab rats, and, judging by his final expression, I would judge that he did."

Penny threw her arms around him. "We're not ever going to talk about this again," she said, and Sheldon patted her back awkwardly, grimacing when he felt her tears dampen the shoulder of his shirt. "And you really, really should not have done that." She pulled back to look him in the eye. "But... thank you."

Sheldon sorted through his choices and settled on the one expression his mother had deemed appropriate for family portraits, and Penny's face softened in answer. Her cheeks were wet. It all made him feel vaguely uncomfortable, tense, but entranced, because no one had ever looked at him the way Penny was looking at him right now.

"I don't know what I'd do without you guys."

Sheldon took Penny's key and locked the door behind them, the door to Penny's cold, stale apartment, and they crossed the hall, toward the cheers of the boys as they strafed their way through another FPS level. Soon Raj would see Penny and clam up, and they'd make room on the couch, order another five-serving meal, and keep her safe.

"Lead a life distinguishable only in its propensity for entropy and disaster," Sheldon replied, and just before he opened the apartment door, Penny slid an arm around his waist for one last squeeze.

And the feeling wasn't entirely objectionable.