Penny and Leonard had a one night stand and Penny ended up pregnant. But rather than telling Leonard about the baby she decided to avoid him completely and vowed he would never know about their child. Yet their friends all knew about him, and saw him almost daily. It was difficult to keep him a secret because Penny didn't have enough money to move away and still lived next to Leonard. She had others tell her where he would be at certain times so he could never see their son. After about 6 months of doing this, Penny decided to finally respond to Leonard's constant attempts to contact her by faking a relationship with Stuart to explain the baby. She then went on to write him a note with the time and place of their meeting so at 4:44 am on April 4th (their sons 1st birthday) he knocked on her door to figure out what was going on and why she'd avoided him for a year and nine months.
"Ummmm… hi…so….uh…um…long time no see right?" Leonard awkwardly started off their reunion.
"Leonard." stated Penny her eyes deep with unidentifiable emotion
"Uh- yeah that's me I mean this is when you wanted to see me right that note was a little vague.."
"There's something I want to show you… the reason that I've been hiding"
Penny walks away down the hall leaving Leonard awkwardly standing in the doorway. A moment later she comes back murmuring reassuringly to the baby boy dressed in star trek pajama's she was holding tenderly in her arms.
"It's okay little man it's okay can you say hi to Uncle Leonard?" Penny questioned the sleepy little one cradles against her chest.
"But Mommy you sad no talk Uncle weonard!" protested the dark haired green eyed child.
"Well Mommy 's changed her mind, I guess you can talk to him" said Penny chewing her lip absently
"Leonard there's someone that I would like you to meet… My son, Oliver… but we all call him Four, because of his birthday, 4:44 AM on April 4th, he's one today."
"Ummmmm well uh- congratulations and happy birthday Four…" Leonard trailed off still trying to process this new unexpected information.
"Well he's tired and he has a big day later," Penny said.
"Okay bye…" Leonard says awkwardly walking away.
Later that day when Penny, Sheldon, Howard, Raj, Bernadette, and Amy take Four on a birthday adventure through downtown LA.
"So today I invited Leonard over and showed him Four." Penny said nonchalantly.
"Oh he must be a happy new daddy" Bernadette sighed.
"Well I'm sure he would be but I didn't exactly tell him that he's his…"
" Well its good that he knows at least because last night I calculated the odds that you could keep him hidden for another whole year and there was a 68.456% chance Leonard would figure out what was going on." Sheldon said mildly.
"Well Four may not be hidden anymore but I don't think that I'll ever tell him whose Four is… Do you think that Stuart will agree to pretend that we… well…ya know…"
"Obviously he will," Howard said in that way of his.
"Oh well good," Penny said looking over at Four playing on the playground in his jeans and a green canvas jacket.
"Is there a reason you dress him just like Leonard?" Amy Farah Fowler asked.
"Well yeah, I guess I want him to have a little piece of his father at least," Penny says.
"Mommy!" Four yelled from where he was dangling on the monkey bars.
Penny starts running over to him but Leonard walks over to him, holds him around the waist and when Four lets go of the bars and then Leonard sets him on the ground. Then Four runs over to Penny and says, "Mommy, Uncle weonard help me ouwn.
"Did he now?" Penny says picking up Four and watching Leonard walk over to them.
"Hello," Leonard says.
"Hi," Penny says with a small smile on her face.
"I see you guys are celebrating little Four's first birthday," he says.
"Yeah we are," Penny says.
"May I join you?" Leonard asked.
"Yes you may," Penny states with a small smile playing at her lips.
The three of them walk back to the group and Sheldon asks, "Are you going to pretend with him?"
"No I'm just not going to tell him," she says.
"But he is bound to find out I mean just look at him," Raj says.
"Well he could also find out if he actually thought about it," Sheldon says.
"Think about what?" Leonard asks.
"Nothing," Bernadette and Penny say at the same time.
"Obviously something," Leonard says as his phone rings and he walks away answering it.
"Mommy, we go to fhe omic wook store?" Four asked.
"Yes of course we can honey," Penny said picking up Four and too the others, "We can all meet back at my place at four."
The answer was a muttering of "Yeah's" and "Okay's"
Then they went their separate ways and Penny and Four headed to the comic book shop.