Little is known about Cindy's life and past before the events of Jimmy Neutron: Boy Genius, except that she has a mom and a dad.

It is known that she moved to Retroville, Indiana and initially found herself the most respected and most intelligent person in her class at school, a position that she used to have. She also began a friendship with peers, such as Libby.

Jimmy took her "smartest person in Retroville" title when he moved into the house across the street from her whereupon Cindy, now second runner up, began a rivalry with him. She used to begin frequently attacks his intelligence by teasing him, playing pranks on him, and by criticizing his every mistake, even though most likely, she only does this to mask her love for Jimmy. She's frequently helped by Libby. Her home life is rarely shown, and her parents are only minor characters in the show. But some of the statements she makes during "Stranded" seems to suggest that she's not very happy at home.

Cindy is a member of the group of five, along with Libby, Carl, Sheen, and Jimmy, who usually go on his adventures with him. She began developing a deep friendship with these five, despite being the most aggressive and critical person in the group.

Penny Peterson, like Cindy, is also very rich and spoiled. She appeared to have been envious of Sherman's smarts and called him a dog and bullied him which resulted into a fight. She may also have a wicked sense of humor and spiteful as she would go far to get back at those she dislikes, as she bullied Sherman and in Egypt, when King Tut threatens to kill Mr. Peabody and Sherman, she says "You'd do that for me?", indicating she may have wanted that to happen out of spite for Sherman showing her up in class.

However, later they form a very strong friendship during their adventure. Sherman has a large crush on her. Penny also seems to have a crush on Sherman as well. So it happens that she and Sherman have a crush on each other. She also is very rebellious, as she tends to stray from Sherman and Mr. Peabody during the time traveling adventures, as shown when she wanted to stay in Ancient Egypt to rule with King Tut and keep his riches once he died, and when she took Da Vinci's flying machine for a test run with Sherman as an unwilling accomplice.

She is also manipulative and greedy, as shown when she wanted to marry Tut knowing he would die young in order to inherit his throne and riches (though eventually backed out once she realized when he died she would be killed and die with him) and when she tricked Sherman into showing her how Da Vinci's machine worked. Despite all of this, she is also shown to be willing to face up to her mistakes, as she proclaimed in front of everyone that it was her fault for provoking Sherman to bite her and that he didn't do anything wrong and attempts to take full responsibility for her actions in order for Mr. Peabody and Sherman to remain together (though this is not enough to convince the cold hearted Ms. Grunion to release Mr. Peabody) and apologizes for everything she has done. This proves not only can she understand her own mistakes, but is also loyal and caring to those she is close to.

But unbeknownst to the 2 girls, there's a secret hidden involving the 2, and one night will reveal it all.

It was a snowy afternoon in the city of Retroville, it was a winter wonderland, and it was beautiful, especially with Christmas coming up, the holidays are usually fun, especially when the Colts are good.

Paramount Pictures & 20th Century Fox Presents

However, for Jimmy Neutron and his friends, Christmas usually means inventive fun with Jimmy's inventions, but this year, Jimmy was unsure what to do after what happened on Thanksgiving.

During Thanksgiving break, Jimmy and his friends and family vacated to Megaville, California, where Jimmy met Dexter, Megaville's boy genius, and they crossed paths with Mandark and Eustace stritch, which would result in a battle with the 2 villians. At first Jimmy and Dexter were reluctant to team up, but they soon teamed up when their friends needed them the most. While there, Cindy revealed her feelings for Jimmy, she was heartbroken when Jimmy saved his friends instead of her (Cindy was saved by Dexter, though), but once Jimmy found out her feelings, the 2 embraced once they saved the world from Mandark's wrath.

A Nickelodeon Movies, O Entertainment and Dreamworks production.

Since then, the 2 have been boyfriend and girlfriend, but they are still trying to find a way to set a date. However, Cindy's family is going to New York City for the holidays for a New Years' Eve party at her rich Uncle's penthouse.

A Robert Minkroff/John A. Davis Film,

Jimmy Neutron and Mr. Peabody and Sherman in...

A Family Secret

However, Cindy hasn't seen her Aunt and Uncle since she was 3 years old, but she barely remembers her Aunt and Uncle, Patty and Paul Peterson, and most of all, she hasn't seen her cousin since then, and her cousin was Penny Peterson, Sherman Peabody's best friend.

But let's get back to the story before we get off topic here, anyway, it was a snowy afternoon in the city of Retroville. And where were our heroes? Well, they were at Jimmy's laboratory, looking for something. Sheen was glancing at all the past inventions, Libby was listening to music, Carl wasn't doing much, Nick was being cool, like usual, and Jimmy was demonstrating a catypult type of invention.

"I present to you, the ultimate snowball throwing machine." Jimmy said, enthusiastically.

Sheen looked at it in awe, and then said, "Cool! What does it do?!"

"Let me demonstrate." Jimmy replied.

Jimmy grabbed a remote control, and pressed a button, and then, in an instant, the machine generated a snowball in the the throwing hole thingy, and then the catepult launched a snowball at Carl, and then after being hit, Carl then replied, "Neat! It's not dangerous, right?"

Jimmy rolled his eyes and chuckles, " No, Carl, it's completely safe."

Jimmy then notices Cindy not paying any attention, she looked kinda worried, so he then walked up to Cindy, and then asked, "Is there anything bothering you, Cindy?"

"Actually, yes. Listen, Jimmy, as much as I want to spend the winter break with you, I can't." Cindy then replied, sadly.

Jimmy then replied in confusion, "What? What's the reason?"

"My parents are having me visit my aunt and uncle and cousin in New York for the holidays." Cindy replied.

Sheen then replied, "Well, be careful in the City of New York, Cindy, because there was a disaster which included a tear in the universe and historical figures were entering the present day timeline, and after it was all cleaned up, it-"

Nick then interupted, "Yeah, about that, I don't think we have a lot of time for any of your makeup stories."

Cindy then replied, "About that, it's actually true. I don't know what happened, but I'm sure I'll find out when I get there."

"Well, I don't know if I could deal with that, especially with him out on the lose in Megaville." Jimmy then said.

Who wouldn't blame Jimmy for worrying about Mandark? Especially when Mandark came really close to murdering Jimmy and her friends.

"He's not coming back, Neutron. I bet Dexter's looking for him." Nick then replied.

Cindy then said, "Well, I'm going to pack my bags, I'm leaving tonight." Then Cindy kissed Jimmy on the cheek and then started to leave.

Jimmy was shocked and saddened by this, what was he going to do about this? Especially with the holidays around the corner.

Meanwhile, it was also snowing in New York as well, and Christmas break was about to begin in the city of lights.

But for Sherman Peabody and his father, Mr. Peabody, they were going to the Peterson's Penthouse for a Christmas Party.

Speaking of which, at Peabody's penthouse, Sherman and his classmates were getting decorations set for Christmas.

Carl, a kid on a wheelchair then said, "This is going to be some party, huh?"

Sherman then replied, "No kidding! Penny's parents have it at that fancy diner, and Penny said that I'm the guest of honor."

Author's note: Penny's parents will have a cameo appearance at the Christmas Party!

Sherman then placed an ornament on the Christmas tree, and then looked at it in amazement, he was excited about the holidays, especially when Mr. Peabody loves the holidays!

Then, sherman heard someone say, "Hi, Sherman!"

Sherman looked behind and saw the love of his life, Penny Peterson, but instead of pink, her dress was red and green for the holidays.

Sherman then said, "Well, I hope you're ready for the Christmas party this upcoming Christmas, Penny."

Penny walked over to Sherman, and blushed as well. She replied, "Of course I am. And I'm so happy that you're coming, Sherman." Sherman then placed the rest of the ornaments on the trees.

Penny seemed to be happy that Sherman was coming to her Christmas Party, ever since that incident with the WABAC a few months ago, Penny and Sherman have been closer than ever, not only that, Sherman's father, Mr. Peabody, has stopped being so overprotective of Sherman.

Sherman then replied, "Mr. Peabody's in the kitchen, making food for the party. Oh, and someone from your family is heading over here for the holidays, right?"

Penny then looked surprise as she heard the sentence. Then she looked away in confusion and worry. Could she know about something that neither her classmates or Mr. Peabody don't know?

Sherman's smile faded, and then he asked, "Are you okay?"

Penny then replied and said, "Oh, um, yes. I'm fine, just a little tired."

Sherman looked suspicious, why would Penny say that she was tired when she got some sleep last night? Sherman then decided to shrug it off and get back to decorating the tree.

Meanwhile, Mr. Peabody arrived in the living room, holding a plate of cookies for the kids. Mr. Peabody said, "Well, I hope you're hungry for chocolate chip cookies!"

Then, in an instant second, all the kids darted after the cookies. Sherman then curiously walked up to Peabody, and then asked, "Excuse me, Mr. Peabody, but have you noticed Penny acting a little weird?"

Peabody's smile then faded, and as he set the plates down on a table, he and Sherman walked over to the right and started to have a conversation.

Mr. Peabody replied, "What do you mean?"

Sherman then said, "Well, during the past 2 weeks before today, she wasn't sitting with me at lunch, don't get get me wrong, she still has her grades are still at straight "A+'s". But she didn't want to spend time with her friends, or me. She's hiding something."

"Well, why don't you talk to her, Sherman?" Asked Mr. Peabody.

"I did, but she didn't want to talk, but it wouldn't hurt to try again." Sherman then said, worriedly.

The boy then walked into the kitchen, as he saw Penny finish up her cookies, she looked tired, so she must've been lying to Sherman.

"What's going on, Penny, I'm worried about you." Sherman said, demandingly, and pointing his finger at Penny, questioningly.

Penny then said, "I didn't want to have a party when my Dad thought of it, but I decided to try to get myself to have fun."

"But why would you lie to me and Mr. Peabody, and most importantly, why would you lie to your parents?" Sherman then said, losing his patience.

"I said I didn't want to talk about it!"

"I'm your friend, I won't tell anyone!"

"I don't care, it's a family secret."

"Just trust your friend, Penny. I need to know the truth."

Sherman has never looked curious than before, he was like a little dog, seeing what's on the dinner table, Penny, on the other hand, was stressed, she was slightly sweating a bit, but she was worried. Then she took a deep breath, and sighed deeply.

"Fine." Penny regrettably said, she continued, "I'll tell you. When I was at the age of 2, my parents were having a barbecue with my Dad's boss. That job got Dad promoted, but you know what the biggest memory of that party was? Not the burgers, not the balloons, it was my long forgotten sister, wanting to be taken into custody of my Aunt and Uncle. So, my father gave custody of my sister to Aunt, and I felt alone ever since, that was until you came along."

Sherman was shocked, along with the other students. Who knew that Penny had a sister, but why on earth would Penny's dad gave custody of one of his daughters to his sister and brother-in-law?

"Penny," Sherman said in shock. "I never knew you had a sister. It must've been tough on you for the past few years."

Penny replied, "Yeah. Well, I better get going, A Charlie Brown Christmas starts at 7 tonight." Penny started to get her coat on and walked towards the elevator, leaving everyone worried.

Mr. Peabody then said, "Woah, that was depressing."

Sherman then replied, "I know what you mean." Then he started to feel worried. "Where did you go, Penny?" He thought. "Swept up by a wave of your own darkness. Where have you gone, Penny Peterson? Wherever it is, go easy, my sweetheart."

Who could blame Sherman for being worried, no one. Her sister abandoned her when she was young, and ever since then, things have been hard for her, she missed her sister. There was no telling where she could be right now. She could be anywhere in the USA.

Cindy's going to NYC for the holidays, and Penny is missing her long lost sister, and with Sherman curious, there's not a doubt that he's going to find out what happened back then! Will Sherman find out the truth? Find out on the next chapter!