Nicky is an Australian mouse who is part of the Thea sisters, an adventurous group founded by Thea Stilton.
Nicky was born in Australia and came to Whale Island to study at Mouseford Academy.
Her friends are Paulina, Violet, Pamela, Colette, and Thea. She has made numerous amount of other friends while on adventures. Nate, Ashivn, Annika, Candy, Giovanni, Yuko, Joshua, Ronaldo, Ivan, Kanuk Krilaut, Grandpa Krilaut, Ernanek, Julie, Holger, Kumi Nakamura, Sakura, Gonzalo, Rhonda Razorpaws, Bridget Macnamouse, Ewan, Shalia, Carlotta, Renani ,Anita and Joaquin are most of the friends she and the Thea Sisters have made.
Her closest friend in Mouseford Academy is Paulina, her roommate. She and Pamela also share a somewhat close bond. Her family owns a ranch back in Australia.
She does have parents, who were mentioned in The Mountain Of Fire, but they are never seen. She has a grandmother - Naya. Billy, Ted and Mitch (fiancee Lily) are Nicky's cousins.
Nicky is a brave young mouselet and loves nature. Although she is claustrophobic and can't sit still, she is very dedicated to the rest of the Thea Sisters, and often performs whatever dangerous stunts may be necessary such as the one she pulled of in The Mystery On the Orient Express.
Nicky has red hair that are tied in pig tails. She often wears a hat (but in later illustrations show that she no longer does), but when she dresses up for an occasion she usually doesn't. Nicky has grey fur. Her usual outfit is a short, blank, orange shirt and wears a green short jacket that is green and has tiny light green and dark green spots on her sleeves, and the sides of the jacket. She wears Australian, brown pants that have zig-zag stitches on them. She also carries a red belt-bag. Her eyes are actually green but in the "Thea Stilton: Mouseford Academy" books and the "Thea Stilton" comics series, her eyes are dark brown.
- Nicky's overall appearance was changed to match the brighter, more cartoony art style of "The Spanish Dance Mission" onwards. The most notable design tweaks are that she no longer wears a hat, and her hair color has been changed from red to auburn.
- The introduction art changed in Thea Stilton and the Tropical Treasure.
- According to the article in Heroes Wiki, Nicky is predicted to be a teenager aged at 15-16 years old. This is probably an assumption made by the writer of the article as there is no clear evidence in any Thea Sister book which reveals her exact and true age.
- In the book The Legend of Fire Flowers, Nicky has a crush on an Hawaiian surfer Renani, who also develops a crush on Nicky.
- In the book The Dragon's Code, it was revealed that Nicky, along with Paulina, are in an organization called "The Green Mice", but in the comics, it is the "Blue Mice".
- Along the book series, she has never been seen using any Australian expression or exclamations such as "g'day", "bloke", "mate", and etc.
- Her most dangerous stunt yet was when she scaled the roof of the cars of the Orient Express with Pamela while it was moving in The Mystery On the Orient Express to catch the Cat Burglar.
- She seems to be somewhat ambidextrous if you look closely at her illustrations in the books.